If it's been exclusively a US car, running both Carfax and Carproof will give you a fairly good picture of the car's history. Carfax and Carproof use different databases for US vehicle information and it's worth running both if you're unsure of a vehicle's history; I've seen one be more informative than the other.
Canadian electronic records are generally less reliable. If you think the vehicle has been in Canada, running just a Carproof search is not enough; also run a search with the provincial insurance agencies, if applicable. I've seen a couple of vehicles with clean Carfax/Carproof reports but with accident history on their ICBC report.
