Back a few years I often imported aircraft into Canada, by air, on trailer and even towed.(probably 2 doz or more)
Same should apply for tractors.
Know more than the customs officer. Research and know your tariff numbers and rules.
The first is probably the toughest as much research is needed.
1- Private imports is totally acceptable. (commercial need a broker unless you have it all down pat)
2- Paperwork, bill of sale, signed is most important.
3- Be able to quote the tariff item #'s
4- Terms such as, 'made in Can, returned to country of origin' is magic.
5- Best deal for a Cdn would be shipping to a US pick up point and the client hauling over the border. that way he brokers privately without all the brokerage fees as long as he has the supporting paperwork.
Services such as UPS, Fedex will add so many fees and taxes that the buyer will wish he had purchased locally in Canada. (Been there, done that!). Cartage firms using LTL rates will also kill all the advantages.
I know you have your own hauling capabilities, so I suggest you team up with a 'border buddy' and drop ship to his facility and let the Cdn buyer pick up and do his own crossing.
With a proper bill of sale he won't have any difficulties importing. In fact, depending on his stay in USA he can be exempt from any duties/taxes. Otherwis, generally he is liable for only the normal local taxes (which vary fron province to province). Either way he will be miles ahead vs purchasing same goods in Canada. (except for Cdn made goods, i.e. Pronovost Puma blowers which are Cdn made goods)
An example; $200 purchase recently made on EBay which should have cost me, ie $18.00 via USPS was sent UPS! The UPS fees were $92.00! That's all brokerage and disbursement fees!
The only way to be econimical is a border drop point with buyer pick up.
Couple years back I bought a used 60" blower for $400. and picked it up in Albany, NY.
With proper bill of sale I cleared the border same day with a disbursement of no more than $25 odd dollars! Not bad for a day's work!