Importing a car into Canada is quite easy. Make sure you have the title for the car. If the car is over 25 years old it is classified as an antique and all you pay is the GST on the value in CDN funds at the border. If it is over 15 years old it is exempt from Transport Canadas rules and you do not have to change anything to meet Canadian standards. I've brought 3 914's back home with me in the last year and never contacted US Customs about any of them. What would they care? The car is leaving their country and they should only be concerned if it was entering the USA. The paperwork and inspection at the border takes about an hour. Canada Customs checks the serial numbers to the title and the build date sticker. Also if you find a great deal take copies of your emails to show Customs that what you payed is the price shown on the bill of sale. If you don't document it, they can access a value. There is a couple of interesting posts on the 914 club site about buying a used car that anyone who is thinking about buying a car should read. Eye opening.
http://www.914club.com/bbs2/index.php?act=ST&f=2&t=2702& and
http://www.914club.com/bbs2/index.php?act=ST&f=2&t=2772&