They sound completely different to me, but I can't say exactly why. Canadian sounds nicer to my ears because it's marginally closer to a NZ accent; a lot of words are pronounced in the English way instead of the US way, like "route" for example.
Down this end of the world we get the same thing with visitors thinking NZ and Australian accents sound the same (don't get started, Paul...) when to us they are so completely different anyone with half a working ear and two tiny brain cells to rub together must surely notice the difference.
For some reason, when I've been in the USA people think I'm Canadian. When I've been in Australia people think I'm English. When I've been in the Pacific Islands people think I'm American, don't ask me why. The prize, though, must go to the person in Washington DC who immediately said, "You're from New Zealand, aren't you?" and when I said yes, stunned by his perception, he answered, "Yes, that's just off the southeast corner of Canada, isn't it?" Aargghh.

Brunnen-"slightly foreign everywhere I go"G