I imported all of mine except my first. It was easy because antique firearms are exempt from US ITAR regulations. BUT - I have recently read that the US has removed the ITAR exemption for antique firearms, and if that is true then you'll probably need to go through one of the import services and it tends to get expensive.
I heard that the US DHS recently has instead made it stricter and harder for Americans to export antiques as they want US dealers who export antique firearms to first get registered as a DDTC/ITAR exporter ($2500 USD a year) and then submit through their DDTC software system (basically registering with a extra fee) the antique firearm and also submit proof that it is in fact a antique and meets their BATF definition of what is a antique firearm.
They have not yet gone after smaller dealers or individuals who may export and ship the odd antique firearm into Canada and are not aware of the increased DHS attention on this as far as I know. I had a US antique firearms dealer who used to ship into Canada who was paid a home and work visit and lengthy interrogation from DHS and threats to take his FFL away about his outside of USA antique firearms dealings that had not been declared and registered with proof as antique with DDTC.
They said that they recognize that antique firearms and some antique parts are exempt from ITAR but he needs to get the antique exemption for each item to ship as a commercial exporter by first joining and registering it as exempt in the DDTC system.
They mentioned in their little talk that Obama and the new Canadian Prime Minister had a recent discussion about tightening the transfer and movement of firearms between the two countries so they (DHS) are now investing more attention on making sure that the transfer of antique firearms is done with no non antique guns slipping through wrongly.
Before all he did was describe the item, declare the value and that the shipped items were antique on his customs declaration forms at the post office.
They wanted him to register as a DDTC exporter and log and submit electronically with all details of the intended person taking delivery of all his firearm related exports and imports, even if they were antique, as they would need the proof he submitted when he filed a export request to confirm that. He told me it is no longer worth the hassle or increased cost and is only shipping within the USA now.
This may all be BS on the part of DHS but they sure scared the dealer into stopping all exports into Canada. Maybe things will change back to the old ways again if Trump gets in, but who knows!