Topskier,
Yes, it can be done, I have one underway now, but be very very careful. You really have to want the American plane - Can you not find what you want already C registered? That really would be your safe thing to do for the first plane.
There are enough differences between the FAA and Transport Canada systems defining an "airworthy" plane, that you can easily get caught in the middle. There are Canadian requirements and limitations, which do not exist in the US, which can result in a completely legal and airworthy US aircraft not being acceptable in Canada, and requiring overhauls. Un approved modifications can be another problem. What's "approved" in the US, might not be so in Canada - different systems.
If you must buy from the US, it is vital that a Canadian AME/AMO inspects the aircraft first hand, and conducts a paperwork review, in the context of the Canadian requirements. Be prepaired to pay that person, and still walk away from the plane. Yes, there is more choice in the US, but I doubt that the cost savings would be so great as to cover the additional costs of informed buying across the border, unless it's a very rare or special aircraft.
Good luck...