i'm currently w/ Rogers so it might make sense to just buy the phone thru them.
Cheers!
If you need the phone unlocked during your contract (i.e. to travel) or you aren't wanting to sign a new contract, get an unlocked one from Apple.ca or from an Apple store. Rogers full price iPhone are $30 cheaper than Apple's, but they are locked to Rogers. And assuming you have no contract, they will charge $50 to unlock which puts you over Apple's price and you have to go through the hassle of talking to Rogers to get them to do it for you.
I am not sure where you are getting that iPhones are cheaper in the U.S. Their contract pricing is actually more than ours (16GB US$199/CAN$159 , 32GB US$299/CAN$269). They do only have to sign 2 year contracts though, whereas ours are 3.
Now, as for their no contract phones, I am not aware of that price. But as others have said, it would still be locked to AT&T. So, with the cost of the phone, the cost of shipping it here, and the fact that you wouldn't currently be able to use it here, it makes no sense to get one from the U.S. Also, I think, but someone can verify, that you have to be an AT&T customer to buy an iPhone (well until the Verizon one arrives which will also be locked and unusable here). So, it's not like anyone off the street can step into Apple or AT&T and pick up a phone unless they have an AT&T account.