I tried to export some old milsurps to the U.S. a few months ago. I was told that there was a U.S. import ban on that kind of stuff, so I dropped the idea and sold them locally.
On the other hand, I've imported several old milsurps from both the U.S. and Switzerland without any problems, which I found odd considering the Canadian Government's anti-gun stance. I would have thought it would be downright easy to ship old stuff south to their "right to bear arms" culture.
I heard someone at our club the other day mention that they thought the U.S. ban might have been lifted, but you should check with ATF down there.
You need to check what you're trying to export against the values U.S. collectors pay, as it might not be worth it depending upon the particular firearm. For example, K31's can currently be bought in the U.S. for about $79 US, while the same gun here would probably sell for somewhere between $250 and $350 Cdn.
BTW, be careful of the brokerage fee costs if you can get an import certificate. I saw some from a few years ago that were half the cost of the rifle. At that time, one broker told me that it was only worth it if you have a shipment of dozen or more guns. Things may have changed, but it's worth checking.
Try Brian #### at BDL. He may be able to help you more...
Regards,
Badger