Check out iPhoneinfo.ca
Lots of great info there about using the iPhone in Canada.
To sum it up nicely though, yes you get the majority of the functionality of the iPhone while using it in Canada.
You will not have access to the revolutionary Visual Voicemail feature, as Rogers is not set up for this. You will also have no direst access to the Youtube functionality. you can get the youtube feature through the safari browswer at Dailymotion - Share Your Videos
The other MAJOR drawback is that you will be gouged on Data if you use anything other than the wifi connection to search the web or download email.
Canada is living in the dark ages where data rates are concerned.
Hope this helps,