Re: Canadian artists selling in the US?
I haven't transported art or sold art between Canada and the US, but in my other life I have delt with a lot of equipment and equipment parts.
I would speculate that you should first make a call to a customs broker and talk with them. I do know that when even ordering replacement parts or equipment componets, I would have to specify and retain a customs broker to be able to pick-up the package from the shipper. I suspect that will be the same for you and the gallery.
The money was easy, bank wire or certified checks.