If I remember correctly from Socials Studies, what it boiled down to in WWI was an Anglo-Canadian government making decisions for the country as a whole without consultation of the Quebecois who felt that they weren't being represented.

The War Museum says this:

French-Canadians, as well as many farmers, unionized workers, non-British immigrants, and other Canadians, generally opposed the measure. English-speaking Canadians, led by Prime Minister Borden and senior members of his Cabinet, as well as British immigrants, the families of soldiers, and older Canadians, generally supported it.

Can't speak for WWII, though. I thought the tensions had sort of evened out by then.