It's a big country and, like America, it has dozens of dialect variations. People who live in Eastern Canada and Western Canada do not share the same Canadian "accent". The same holds true for America, right? People who live near the Canadian-American border might share a similar speech pattern; that is, the Americans probably sound Canadian, or is it that We sound American?
Mind you, you can pick 'em out quite easily 'cause Canadians say, "Eh?" and Americans say, "Huh?" TV is also a major influence; children these days watch more TV than they did in the past; the days when mother was the primary language and care giver are over; TV has taken that role; it and the 300 or so "American-accented" channels it has to offer. It's not quite that easy to tell the difference between a Western Canadian actor and an American actor. Western Canadian actors sound slightly different - psst, isn't Brad Pitt from B.C.?; Eastern Canadian actors sound very different, though. They have the "oo" thing going; you know, "aboot" <about>.
Again, "accent" is the thing. Grammar, syntax, and vocabulary are on par with, if not equal to, our American cousins'.
Is there a difference between American English and Canadian English? All one has to do it watch the National News at 6 p.m., ahem, in both countries.