The following is a link to the BC Supreme Court's decision on Canada's Polygamy Law, which was challenged by (among others) the Canadian Polyamory Advocacy Association on behalf of polyamorous Canadians:
The Judge's decision makes a distinction between formalized poly unions and common-law cohabitation, the former being illegal, still, under the law.
Here is the CPAA's official reaction to the ruling (from their website):
Polyamorous people should be disappointed at this decision because, while it recognizes that there are some poly relationships that are NOT patriarchal, harmful and inequal, it does not decriminalize full expression of these relationships.
With these clarifications, it would seem the battle for legal recognition of ALL forms of polyamorous, adult, relationships has only begun..