I gotta say GBay, specifically Massassauga. Endless amounts of habitat, lack of fishing pressure, access to big water and massive amount of feed.
Although, upper Niagara holds quite a few fish My oldman tied into 2 muskie's fishing for smallmouth bass a few yeas back, landed one 38lbs, 45inch 5 mins later had another one on even bigger, broke the line. This was on bass tackle, lol we were fishing for smallmouth 6lb test, little hooks, small minnows...
I know the lower Niagara has some big fish, atleast one or two big fish (40lb+) get caught during the St.Catharines Salmon Derby at the mouth of the river...
This is all based on personal opinion