Canada

Federal law defines marriage as the lawful union of two people, exclusive of all others. Criminal Code provisions prohibit bigamy and participation in a form of polygamy or a conjugal union with more than one person when a rite, ceremony, contract or consent purports to sanction it.

A 2011 British Columbia Supreme Court reference interpreted that offence as directed to marriage-like sanctioned unions rather than mere multi-party unmarried cohabitation. It is an important but jurisdictionally limited decision, not a national declaration that every informal arrangement is risk-free.

Provincial rules differ sharply. British Columbia gives some marriage-like cohabitants spouse status and expressly handles two or more surviving spouses in succession. Ontario's statutory matrimonial-property equalisation remains primarily for married spouses, and common-law partners do not ordinarily receive the married-spouse intestacy share.

Any multi-adult household needs province-specific advice on whether concurrent common-law relationships are recognised for the particular statute involved.

Ontario has a genuine statutory route for pre-conception agreements involving two or more intended parents, normally up to four parties, plus court pathways for larger intended-parent groups. British Columbia permits defined three-parent structures in particular assisted-conception arrangements.

These are parentage rules, not group-marriage rules. Timing, conception method, consent and written-agreement requirements are decisive. Joint adoption generally remains limited to one or two applicants.

Federal family sponsorship recognises one spouse, common-law partner or conjugal partner. Several adults cannot be sponsored together as one partner group.

Healthcare authority is provincial. Ontario uses a ranked substitute-decision hierarchy and allows multiple attorneys. British Columbia representation agreements may also appoint several representatives and allocate authority among them.