http://www.cbsa-asfc.gc.ca/E/pub/cp/.../rc4044-e.html
you must also comply with transport canada rules in concert with customs dept.
it would seem that anything newer than the last 15 years has to be on a special list or it can not be imported and there are exceptions ( ie: living there and bringing car home, etc.) and it differs for countries other than the US.
However , farm tractors are duty free except for GST and/or provincial taxes...and this was from the gospel word of a Customs officer.
Sean