There is a river in Spain where the Wels catfish was introduced where they are not growing over 400 pounds... That's a big fish! If I recall correctly they must ascend rivers to spawn.

I suspect even channel cats and more likely blue cats would struggle to survive all but the most southern portions of BC. Channel cats range as far north as southern Canada in the Mississippi drainage and blue cats don't make it that far. I suspect channel cats could survive in perhaps the southern 1/3 of BC by their growth rate would be very slow. Other than a large number of trout and salmon species, a few minnow and sucker species and a scattered mix of other oddities like burbot and sturgeon, not much is native.