I have no idea what goes on in Black churches, since I have never attended one. But, I have heard that it is discussed. I have seen literature in Catholic Church vestibuls on which candidate support "pro life". But there have always been preachers, priests and other lay officials that have marched in demonstrations and otherwise took part in political events. My point of view is that churches need to tend to the spiritual needs of their flock, and refrain from political participation and comments. Seems to me that tending to people's spiritual needs would be a big enough job without getting involvd in who they vote for.
But, I don't want to get into a religious discussion. Marriage is still a civil contract- you need a civil license to get married and if you get unmarried you need to divorce through the legal system. Whatever other ceremonies and such connected with your (or anyone else's) church is another ball of wax. Just like there is a difference between your spiritual morality and what is legal.
I don't give a darn about what is going on in Canada. Their laws differ significantly from ours - just like any other country in the world that permit civil unions. Canada is not the U.S.