Some statistics on the .455/second model:
Serial number range 5001 - 74755, so about 70,000 were produced.
The majority went to the British. The Canadian government purchased 14,500 directly from S&W, according to Neal & Jinks. Roy Jinks in HOS&W also observes that the Canadians bought a total of 724 revolvers chambering the .45 Colt cartridge, but the specific serial numbers were not recorded.
There are a few commercial models, some of which were distributed in the United States. I half-recall (but don't completely trust my memory) that a few dozen .455s with high serial numbers -- maybe the last ones in inventory -- were shipped to a Midwestern City. St. Louis? Kansas City?
I can believe that revolvers in the commercial Canadian market may not have been subject to proof marking, but what was the situation with direct-purchase Canadian revolvers that were eventually released to private use? There is a crown-over-30 stamp on the butt of my .455/second, as well as a crossed-pennant stamp on the left side at the rear of the frame. Not the tidy, small, deep stamp familiar from British revolvers, but a larger stamp that was half polished off when my gun was refinished. Photos:
ADDENDUM: On reflection, I realize that I am confusing proof marks (which these are not) with acceptance marks (which these may well be).
Where on earth did you find it?? 
Have you lettered it yet? I wonder if it shipped to a Canadian Distributor....
