Oh I hope I didn't make a thread like this before, but I just came back, so I'm not sure.... 

 For example, if I purchased a ferret in Minniapolis, would I be able to bring the ferret back into Canada? If not, which vaccines would I need to get first? Thanks! :D

It seems to depend on where *you're* from.
Are you Canadian, or do you at least currently reside in Canada?
If you do, all you seem to need is proof that the ferret(s) has/have been vaccinated for rabies in the last year. 
If you don't live here, apparently the border guards may quarantine your ferret(s), but it's at their discretion. (In other words, be nice and polite and agreeable, and you should be fine. Be belligerent or rude and you might find yourself facing a quarantine, and possibly a cavity search)

That's coming from here www.inspection.gc.ca/english/anima/imp/petani/mustele.shtml with the addition of some personal border-crossing experience. 

Good luck and happy travels!

Thanks you for answering! :P Yes, I do live in Canada, and we take occasional trips to the states. Will a pet store usually give me these verification sheets? (no ferrets in stores near me, so I'm not sure). I know that shelters usually give them, but just in case...