Jurisdiction to handle child custody matters, which are referred to in some Canadian provinces (British Columbia and Alberta) as "parenting" or "parentage" matters or as guardianship matters (e.g. Saskatchewan), rests in part on the Canadian federal law and in part on provincial law.
A. Canadian Federal Law
The Divorce Act of Canada regulates the initiation of divorce cases in all provincial courts throughout Canada.
If a case for divorce is properly brought in a Canadian provincial court, the Act contains provisions allowing child custody issues to be determined within the divorce case.
Thus, the starting point for such custody jurisdiction is whether the parties are married and whether a divorce case can be initiated. Section 3 of the Act provides that a court in a province has jurisdiction to hear and determine a divorce proceeding if either spouse has been "ordinarily resident in the province for at least one year immediately preceding the commencement of the proceeding."
Section 4 of the Act provides that such court then has jurisdiction to deal with "corollary" matters --which are expressly defined in Section 2 of the Act to include "custody" matters -- provided that either spouse "is ordinarily resident in the province at the commencement of the proceeding" or both spouses accept the jurisdiction of the court.
Section 20 of the Act provides that Divorce Act orders have effect throughout Canada and may be registered in the court of any province and be enforced as an order of that court.
B. Laws of Canadian Provinces
If the parents are not engaged in a divorce case in which child custody is also an issue, a parent can initiate a case for child custody under the statutory or common law of a Canadian province.
a. Common law
-At common law, Canadian provincial courts had custody jurisdiction if the child was present, resident, or domiciled in the jurisdiction at the time proceedings were commenced. Most Canadian provinces have enacted legislation that defines custody jurisdiction in place of the common law principles. However, some provinces have not enacted such a law and they continues to apply the common law rules. See e.g. Detcheverry v. Herritt, 2013 NSSC 315.
b. Parens Patriae
-Canadian courts also have "parens patriae" jurisdiction, under which the sovereign authority is understood to have an inherent and overriding power to take actions necessary to protect children. For example, in one case a court in Ontario accepted jurisdiction over children in Saudi Arabia who had previously lived in Toronto, had then moved to Saudi Arabia, whose mother had returned to Canada with only one child and had been left in Saudi Arabia where there was no evidence that the courts would protect them. Johnson v. Athimootil, 2007 CanLII 41434 (ON SC).
Generally, in order to exercise parens patriae jurisdiction, there must be a legislative gap which requires the Court to exercise its discretion. Beson v Director of Child Welfare, 2 SCR 716; RR v Alberta (Child Welfare Appeal Panel), 2000 AB QB 1018, 267 AR 249. Parens patriae cannot override express statutory authority: JU v Alberta (Regional Director of Child Welfare), 2001 AB CA 125 at para 7, 281 AR 396.
-In Ontario, the rules are contained in Sections 22 and 23 of the Children's Law Reform Act. Those provisions are as follows:
22. (1) A court shall only exercise its jurisdiction to make an order for custody of or access to a child where,
(a) the child is habitually resident in Ontario at the commencement of the application for the order;
(b) although the child is not habitually resident in Ontario, the court is satisfied,
(i) that the child is physically present in Ontario at the commencement of the application for the order,
(ii) that substantial evidence concerning the best interests of the child is available in Ontario,
(iii) that no application for custody of or access to the child is pending before an extra-provincial tribunal in another place where the child is habitually resident,
(iv) that no extra-provincial order in respect of custody of or access to the child has been recognized by a court in Ontario,
(v) that the child has a real and substantial connection with Ontario, and
(vi) that, on the balance of convenience, it is appropriate for jurisdiction to be exercised in Ontario.
R.S.O. 1990, c. C.12, s. 22 (1).
(2) A child is habitually resident in the place where he or she resided,
(a) with both parents;
(b) where the parents are living separate and apart, with one parent under a separation agreement or with the consent, implied consent or acquiescence of the other or under a court order; or
(c) with a person other than a parent on a permanent basis for a significant period of time,
whichever last occurred.
(3) The removal or withholding of a child without the consent of the person having custody of the child does not alter the habitual residence of the child unless there has been acquiescence or undue delay in commencing due process by the person from whom the child is removed or withheld.
Serious harm to child
23. Despite sections 22 and 41, a court may exercise its jurisdiction to make or to vary an order in respect of the custody of or access to a child where,
(a) the child is physically present in Ontario; and
(b) the court is satisfied that the child would, on the balance of probabilities, suffer serious harm if,
(i) the child remains in the custody of the person legally entitled to custody of the child,
(ii) the child is returned to the custody of the person legally entitled to custody of the child, or
(iii) the child is removed from Ontario."
-In Quebec the Civil Code provides that, "The Québec authorities have jurisdiction to decide as to the custody of a child provided he is domiciled in Québec." Civil Code, Article 3142. Article 75 of the Code provides that "The domicile of a person, for the exercise of his civil rights, is at the place of his principal establishment."
Article76 provides that, to change domicile, a person must actually reside in another place and must have the intention to make it the seat of his or her principal establishment. The proof of such intention results from the declarations of the person and from the circumstances of the case. Section 77 provides that "The residence of a person is the place where he ordinarily resides; if a person has more than one residence, his principal residence is considered in establishing his domicile."
Articvle 80 of the Code provides that, " Article 80 of the Code provides that, "An unemancipated minor is domiciled with his tutor. Where the father and mother exercise the tutorship but have no common domicile, the minor is presumed to be domiciled with the parent with whom he usually resides unless the court has fixed the domicile of the child elsewhere."
The Code also provides that, "Even though a Québec authority has jurisdiction to hear a dispute, it may exceptionally and on an application by a party, decline jurisdiction if it considers that the authorities of another country are in a better position to decide." Civil Code, Article 3135.
The jurisdictional rules in Saskatchewan concerning child custody mirror those in Ontario in most - but not all -- respects. Section 15, Saskatchewan Children's Law Act, 1997.
One important exception is that custody jurisdiction in Saskatchewan can be based solely upon the parties' having consented to it. (Section 15 (c).
In addition, while Saskatchewan's definition of habitual residence is the same as Ontario's, the Saskatchewan law provides that if the child's habitual residence cannot be determined pursuant to the regular provisions, the child is to be considered as habitually resident in "the jurisdiction with which the child has the closest connection."
f. New Brunswick
The jurisdictional rules in New Brunswick concerning child custody mirror those in Ontario (Family Services Act, Section 130).
g. Nova Scotia
Nova Scotia has not enacted any law that specifies the terms under which it may assert child custody jurisdiction, except that Section 32A of the Judicature Act simply authorizes the Supreme Court (Family Division) to exercise jurisdiction in relation to custody and access to children and parens patriae jurisdiction.
Accordingly, the general common law rules apply in Nova Scotia. Detcheverry v. Herritt, supra.
Alberta has not enacted any law that specifies the terms under which it may assert child custody (parenting) jurisdiction.
Accordingly, the general common law rules apply in Alberta. M. (L.C.) v. S. (P. N.) (2008),  1 W.W.R. 299, 2008 ABQB 459.
i. British Columbia
Section 74 of the Family Law Act of British Columbia contains rules concerning jurisdiction in parenting matters that parallel those that are provided by the Ontario statute (though with some language variations).
Manitoba has not enacted any law that specifies the terms under which it may assert child custody (parenting) jurisdiction.
Accordingly, the general common law rules apply in Manitoba.
k. Prince Edward Island
The jurisdictional rules in Prince Edward Island concerning child custody mirror those in Ontario (Children's Law Act, Section 12).
l. Newfoundland and Labrador
The jurisdictional rules in Newfoundland and Labrador concerning child custody mirror those in Ontario (Custody Jurisdiction and Enforcement Act, Section 28).