2007 has seen the Canadian dollar appreciating significantly against the US. This leads to many people speculating on taking advantage of cheaper car prices in the US. Below are some links to information about the process to help you if you are considering the idea.
Registrar of Imported Vehicles
Article from Canadian Driver
Just a heads up, last time I came back from a road trip to the US, the Canadian customs agent took one look at my car ( 2004 Mercedes Benz E320 Wagon) and promptly asked me if I had any auto repairs done to it in the US.