Canon de Surete translates as "safety barrels". Often seen on French guns. Double epreuve is double proof, which means it was proof tested with higher pressure loads than a standard proof. That's a good thing.
Pricing French doubles is pretty tough. Good shots of the wood (stock and forend) would help. A better shot of the barrel flats--the underside, under the chambers--might help us decypher some more of the French. Good shot of the receiver to show the engraving.
You'll look long and hard to find a "twin" to your gun. Lots of French guns are pretty unique, at least as far as the examples that reach the States are concerned. The French never made much of an effort to export their guns to this country. Quite a few were picked up by GI's during WWII and came home in duffelbags. But with a very few exceptions--one being Manufrance, which was more or less the Stevens of French doubleguns (in terms of quantity, but with a lot higher quality), and another being Verney-Carron--most of the French guns we see in the States are one of a kind.
