New Seaway is one of the best places for fish in the city. I have bought fish from them several times, and yesterday got some sushi grade tuna and crab, and some unagi. We made tuna tartare which was absolutely delicious, crab rolls and unagi sushi. All of it was super fresh and good quality. The prices are reasonable too.
The people who work at New Seaway are really nice and helpful. This is my first choice for fish in Toronto.