Cnose, you have a problem common to many of us. Steel shot is just not compatible with many older shotguns. One potential answer is to have a gunsmith open up the choke to prevent the "ringing" of the barrel, but that is not always desirable or successful. A lead substitute is required to duplicate the old waterfowl loads.
Unfortunately, bismuth shot or shotshells are no longer available. In factory loaded ammo, the only currently available non toxic lead substitute load is the Kent tungsten matrix line of shells. They are beautiful, they work as well as (or even better than) lead and they can be shot through older, full choke barrels. The catch is that they cost about $4.00 per shell. Expensive, but the best shell available.
The only other choice that I am aware of at this time is Nice Shot. Note that Nice Shot is available only as a loading component - you have to load your own shells. Nice Shot is a direct substitute for lead (by weight) so you can use any loading "recipe" that uses lead shot, and substitute the equivalent weight of Nice Shot. This stuff is only slightly harder than lead (it is a tungsten - iron - tin alloy) and thus can be used in full choke barrels, although I don't think I'd use it in fine, thin walled or Damascus barrels. $60.00 per kilo + tax + shipping. About 28 shells per kilo at 1 1/8 oz. per shell.
So, unless someone else knows of lead substitute shells or shot currently available in Canada (Hevi-Shot Classic Doubles does not seem to be sold here), those are your choices.
Sharptail