How to use my iPhone in Canada?

I have an AT&T iPhone 5 and it is unlocked. I'm only gonna be in Canada for week, and would like to know what's the best (preferably cheapest) way to get service up there? I just need a bit of data to use maps to get around and iMessage.

No need to do anything! Cell phones work everywhere in any country. Just make sure your service provider (AT&T) has cell towers up there.