... Canada doesn't fucking EXIST in the DCU ... Marvel at least had a team up here. DC didn't even give us a member of the Global Guardians.
Your Obedient Serpent intuited the obvious: since Shuster modeled Metropolis on Toronto, DCU Canada was obviously annexed by the DCU U.S. at some point in the 19th Century.
This explains where they put all those extra cities; they took all those funny Canadian names and replaced them with more prosaic, descriptive ones. "What the heck's a 'Vancouver'?" "It's a city on the coast." "Can't we just call it 'Coast City', then?"
It's not that DC doesn't have any Canadian heroes; it's that MOST of their heroes are Canadian!