Like the Win man says! Get yourself a Canadian-friendly FFL dealer, I'm sure most of them are earning less money these days and would be more than happy to be educated about Canadian antique laws and a new source of revenue. Get yourself the antique letter from the RCMP, based on GB pictures / descriptions, send it down to accompany the package back to you, and trouble should be little if any.
Just another warning though: I just got a GB-auction package that took 2 months in the mail, tracked into Canada on the second day and shipped priority mail, properly declared etc. Disappeared and untraceable after that. No sign of customs ever seeing it. Things are getting quite silly. A few of the really decent sellers are getting nervous to ship to Canada because of crap like this, they're worried about getting bad feedback compliments of an increasingly idiotic postal system. Just in case there aren't enough problems here yet.
Good to have friends down there, or FFLs, or someone in the firearms export business. Even the exporters don't charge more than $75 for an antique firearm (at least the ones I know), my FFL charges much less than that.