The Supreme Court has answered three of the four questions asked of it by the Governor in Council concerning same-sex marriage:
My short and completely unofficial summary:
Yes, Parliament has the authority to define marriage, for civil purposes, as "the lawful union of two persons to the exclusion of all others," and this definition is consistent with the Charter. It's up to the provinces to say who can/may/must perform marriages, but the Charter protects people from being compelled to perform marriage ceremonies that conflict with their religious beliefs. The Court declined to say whether a requirement that civil marriages be between persons of opposite sexes would violate the Charter; I don't think they want to answer this one except in the context of addressing a particular challenge to a specific existing law.
No surprises in any of this, but it's good news nonetheless.
(Yeah, I'm on mailing lists for both the Canadian and the U.S. Supreme Courts. But it's not like I'm obsessed or anything....)