Until you post clear photos we won't be able to effectively help you. If it's a faked commercial shotgun that someone has converted into a trench gun it will likely only be worth a few hundred bucks... But if it's a legitimate military example, it will be worth more than what's been quoted above. Post war rebuild M97 trench guns routinely sell in the $1500-$2000 range so if it's truly an original untouched WWII example, it will be worth substantially more than that. There are very few originals in Canada so it's tough to say what they're really worth, given that they rarely hit the open market. But, in the United States, examples in superior condition have sold for $10,000-$12,000 at auction. Just look up a few old catalogues from Rock Island if you really want to make your head spin.
