I don't know about taxes & tarrifs on parts purchased in Canada, but this site should help with current exchange rates:
http://www.xe.com/ucc/
They have a currency exchange station just across the border, many businesses take American money, but often give Canadian change and some U.S. banks also do exchanges and have current rates.
If I recall, if you buy more than $200 in many Canadian goods, bring all the receipts and you can get one of the taxes refunded at the border when returning. (Called GMT or something like that.)
Locomotion Racing
http://www.geocities.com/locomotionracing