Yesterday I watched this three-part series on the accents of English-speaking North America:
The videos are by dialect coach Erik Singer and, I must say, his ability to fluidly move through all of North America's accents is incredibly impressive. As I was watching the videos, I kept thinking to myself, "I don't know what this guy actually sounds like when he's not putting on an accent."
The interesting thing about accents is that they really speak to settlement and migration patterns. In other words, who came in contact with who, and who didn't come in contact with others? Geographic isolation also leads to unique accents.
The other ingredient is time. The reason the UK, for example, has so any regional accents is that it had the time for them to develop. On the other hand, if you look to most of the southwestern United States, there is broadly a kind of generic American accent (with the exception of some California and Utah nuances according to Erik). This is because these settlements are relatively young compared to say the northeastern US.
For Canada, the defining feature is "Canadian raising". It is what leads to the stereotype of us saying things like "aboot" and "hoose". It doesn't sound exactly like this, but there is a way in which we tend to pronounce diphthongs (two adjacent vowel sounds) with open-vowel starting points.
Open-vowels are sounds where our tongue is positioned as far as possible from the roof of our mouth. If you try saying "about" to yourself out loud right now you'll notice that this is what happens. Your tongue drops. And it is these instances that lead to "Canadian raising".
The other thing that I find fascinating is how quickly language convergence can happen. I lived in Philadelphia for 3 years (for grad school) and when I would come home my parents used to tell me that I sounded fully American. I guess subconsciously we feel a need to assimilate.
If you're also fascinated by accents, I highly recommend you check out Erik's videos.