What is exactly the difference between a Canadian and American accent?
I've just come back from a 5 week holiday in Australia and I know I confidently can say I know the difference between an Australian accent and a New Zealand accent. I knew it before I left kinda but I definitely know it now. If a New Zealander spoke to me I would detect his accent within a few sentences easy. Their constant mis-pronounciation of replacing any vowel with an 'I' where possible becomes apparant. Excellent becomes 'iggcellent' an accent becomes iccent, special becomes 'spicial', batter/better becomes 'bitter' etc. It becomes dead obvious after a while.
Canadian and American I can't though?

On the way back I was in Dubai, and I spoke to a guy to a Canadian guy who I thought was American but then told he was Canadian (from Saskatoon). I ended up speaking to him for a few hours and I couldn't figure out for love nor money where his accent was supposed to different exactly to rest of Americans. I tried hard but I couldn't.

My father was born in Canada and I feel quite embarresed to not know the difference. I'm usually quite good at understanding accents, but the difference between American/Canadian is some of the hardest I've come across at distinguishing. About 98% of Irish people wouldn't understand either probably.
Could someone tell me what the difference is supposed to be? Do they even have one? If that Canadian guy was speaking to an American, would an American know that guy was Canadian within a few sentences? Is it that different?