I think that Canadians handle marriage exactly backwards. We treat marriage as a pseudo-religious union which happens to confer legal benefits - for example - inheritance rights, income tax, medical coverage, pensions, etc. Canada is fortunately more enlightened than a lot of countries.

Where this issue gets confused is the emotional attachment to the term "marriage". Take this word out of the equation. All partnerships between loving adults are equal, without reservation. 

As simply as I know how to put it:

The legal benefits that are currently granted by marriage would then be granted by the civil union. "Marriage" would grant no legal rights whatsoever.

For example:

My wife and I are joined in a civil union per the province of BC and because of this we enjoy the normal benefits you would expect. She is my beneficiary, we automatically have full custody of any children resulting from our civil union, etc. However we would not call ourselves "married". We would have no rights more or less than we do presently.

My friend Adam and Bill have been in a long term partnership and decide to spend the rest of their life together. By entering into a civil union through the province they are granted legal status as are any partners in Canada. The decision as to whether they get married in their local church is between them and the church. If it's a church that allows such things then no worries and if not then they can find a new church, simply put. However they most certainly can file their income tax together, adopt children together, etc.

Putting this all a different way: