You can have a Blackberry with any mobile carrier (Rogers, Verizon, AT&T, Bell, Telus...)
Blackberries are SMARTPHONES, which means you can only sign up for contracts with them. You will need a good credit rating and contracts tend to be pretty costly each month (on average $200 per month) so I suggest you say screw the Blackberry and go get a really cool prepaid phone. Besides, you can't even send or receive video and picture messages on the damn things.