Before leaving the US with your purchase.

Here are some details about the importation process from the US side. I found this on the Edmonds site at
http://townhall-talk.edmunds.com/direct/view/.ef18c13/478

I picked out a relevant quote:
"I have imported cars twice through the Pac-Highway truck crossing(Vancouver). I simply phoned the US border office and asked them to fax me the proper form(import worksheet), I received back details of office hours and procedures along with the form. The American side demands three business days. Simply fax them the info, check that they received it and take a 3 days to get to the border. Pac-highway crossing for example states that you arrive no later than 3.30 pm at the American side. The Can. side is open I believe a bit later. Both offices handle vehicle exports Monday to Friday only"

More later.

G