I imported my 80 Bronco less than a year ago and all I needed was a "Certificate of Title", temp insurance to get it here on the Canadian side (you will also need temp insurance in whatever state your in in the US if you drive it back), “bill of sale”, and then pay the GST at the boarder on whatever you paid for it. I think that was it. Its always good to have a chat with one of the Canadian customs guys before you go down to make sure you got everything to bring the vehicle back.
If its less than 15 years old you will have to pay extra duties on it at the boarder, and if its newer than 1991 it will have to have daytime running lights installed if it doesn’t, along with a speedo that’s in KMs and than a Federal and Provincial inspection. This all has to be done before you can insure the vehicle with-in 45 days or it has to go back to the states.
I have no idea about importing Canada to the US.