Finest Japanese Restaurant
Katsura has a good mix of different food, not just focusing on sushi and sashimi or teppanyaki. See link below.
I guess it depends on what you are looking for. If you are looking for variety, then Katsura would be a good place. If you are looking for a great omakase experience, then perhaps Sushi Kaji is a better place to go. You are going to get very different opinion on this topic (happened many times before) so the more you can narrow down, then the better recommendation you will get.
As SaladKingFan mentioned, you are likely to get as many recommendations for Japanese restaurants as there are people on this board. That being said, if you are looking for the finest, I believe most would agree that it would be among Sushi Kaji, Hiro Sushi and Omi. Jacob Richler in the National Post did a sushi roundup a couple Saturdays ago, but unfortunately they don't keep stuff online that long. He basically concluded that all three were 'superb'.
Both Richler and Toronto Life have repeatedly declared Sushi Kaji the top Japanese restaurant in the city, but I think a more important deciding factor would be your location and in what area of the city you wish to dine.
I have tried different sushi restaurant and I still prefer Katsura mainly because it has move variety of sashimi and sushi than others. For example, sayori is of season at this time of the year and you could find it in Katsura. If you are brave or adventurous enough, you could also try kani miso.
They dont have omakase but you could sit at the sushi bar and ask the chef to give whatever he thinks is good for that day. I do that every time I go there and once I was offered to try the chin meat of a large tuna.
The best Japanese restaurant in Toronto by far is Kaji in the unromantic and gross location of The Queensway and Islington. There are three menu only $65, $85, $125. It's a real experience! The best sushi if that's all you want is Hiro Sushi on King St. Both these restaurants are very expensive but excellent and very authentic.
Kaji is right on the ball.
Hiro - i had sushi there, it was not very fresh that time and lacked flavour. the cooked food i believe is what they are known for.
Yamato - i like their sushi a lot, quite authentic. don't care much for the teppanyaki though.
i am from vancouver so i am super picky about sushi.