I can pretty much guarantee that this is due to customs/import charges. Consumers will cancel orders over a surprise bill from that, a big business won't care at all or will have their own broker.

I could be confusing them with DigiKey, but I think McMaster handle customs themselves, no customer action needed.

If that's a problem to them, I'm guessing they don't have a fully automated solution to that like e.g. DigiKey does.

Were you ordering as an individual? They definitely ship to small businesses on both sides of the border, but might be leery of an individual handling the customs stuff properly. Maybe solve that with a UPS account?

FWIW, one of the benefits of Fastenal is being able to walk in and browse the shelves (just ask them when they're not busy. Never had a problem)

idk. they made me get a commercial account. and their stock for my local shop leans heavily towards grade-8 construction fasteners and not the smaller machine screws that I generally use.