Specifically, grounds for voidable marriages can be waived by cohabitation after the condition is discovered or remedied. (divorcesource.com)
For greater certainty, a marriage is not void or voidable by reason only that the spouses are of the same sex.» (slaw.ca)
The argument here would be that this lack of capacity renders a marriage voidable only, with the upshot that it can only be challenged by one of the parties and is valid until successfully challenged by an annulment proceeding. (slaw.ca)