Then it's a matter of doing some research and shopping around a bit. The Tokina is a little less costly, but it also has less range and can be hard to find. Plus some folks report flaring issues. The Canon 10-22mm is less prone to flare. I have one and I love it.
Check out the
Lens Sample Photos on POTN. Look for both lenses and see which one you like better. You can also read some good reviews on them at
The Digital Picture.