I should have mentioned that one of the rifles I imported was bought from Joe Salter. I merely send them payment and tell them to ship it to Leroy's in Montana. No problem. They already have Leroy's FFC on file.
Another rifle I purchased from another seller in the US I didn't even mention I was from Canada. I merely told them to ship it to Leroy's. Most sellers won't care where the buyer lives just so long as they ship it to a FFL dealer in the US.
If it is an antique, I just tell them to ship it to a US address near the border and I clear it through customs myself. I spoke directly with BATF and the fellow told me that they do not regulate antique firearms. (i.e., you don't need to go through an FFL dealer and you don't need a US export permit.)