I'm not a sushi fan myself, but I'm told by sushi fanatics that Nami & Fune are the best in town. I've been to Nami before (had Tempura). Must admit the sushi looks interesting. They've got these 3 guys that make it fresh in front of you - there's a definite art to it! It's quite impressive to watch them work. At the front of the restaurant they have all the fresh stuff on ice so you get to see what it is you're eating before it's carefully crafted into tempting morsals.
For Dim Sum, in fact for Chinese food in general, Lai Wah Heen is the pinnacle and THE standard to beat. You simply will not find better Chinese food anywhere in North America. (Trust me on this.) As you can imagine, the prices at Lai Wah Heen are higher than normal, though not exorbitantly so. They've got the normal Dim Sum fare there at slightly higher than normal prices. But if you go there, treat yourself to some of their own creations; at $3.50 per piece it adds up pretty damn quick but it's worth it at least once in your life. For a more normal Dim Sum experience, across the street in the Colony hotel you'll find Bayview Gardens. It's down in the basement - don't let that scare you away. Once you're in the restaurant it's fine and the food is quite good.