Well as a Canadian I can usually tell depending on where I go. Canada as a whole has a uniform accent except for french speaking or Maritime provinces(who sound weird as hell). But for the most part the metropolitan areas sound just like all the big north American Cities that aren't in southern states.

There is also some differences because Canada did not adopt the American pronounciation of certain words like "either". Also color is "colour" in Canada. It can be impossible to tell sometimes though. Canadians are quite vocal about being canadian though, so you can usually find out with a simple conversation.