Sorry, I don't have either one, though I tested them when I bought my 12-24 Tokina.
IMO, in some respects the Canon is the best of the UWA. It's very resistant to flare, which is always somewhat of a concern with really wide lenses. The 10-22 handles flare unusually well. Yes, it's a little plasticky. But no EF-S lens will ever be an L-series anyway, since part of Canon's definition of an "L" is that it must be fully compatible with all EOS cameras and EF-S lenses are only usable on croppers from the 20D/Digital Rebel onward. And, IQ is my main criteria anyway (some of my other non-L Canon lenses are a little plasticky, but take great pics and have proven to be plenty durable). On the other hand, the 10-22 is also about the most expensive of the UWA options. (If it were an L, it would be even more expensive, I'm sure!) For the money they charge, Canon should throw in a lens hood at least. But they don't... so figure on a little more $ for that, too. All the other UWA options include a lens hood. Figure on about $890 for 10-22 and hood.
The Tokina 11-16 is plenty sharp and quite well made. It is more confidence inspiring, though the build may or may not actually make it more durable. I doubt it's any better sealed.. It doesn't offer USM, but in one respect that doesn't matter because even a micro motor gives almost instant focus when the focusing group of the lens only needs to move a very short distance to achieve focus. Not having USM, you don't get Full Time Manual Focus (FTM). That only matters if you manual focus a lot. With the Tokina and other non-USM lenses, you have to shift or switch the lens to manual focus before you can manually focus.
How much do you really need f2.8 on an UWA lens? You "pay a price" for f2.8... This lens is probably the most prone to flare and certainly the narrowest range of focal lengths, of any of the UWA options. It's also about $100 more than the Toki 12-24, though it's still considerably less than the Canon... about $700. I simply could justify the trade-off to get the larger apertures, don't see myself needing f2.8 on an UWA, am usually stopping this type of lens down rather than using it wide open. Someone shooting in low light a lot might want f2.8, though.
I found the Tokina 12-24/4 a nice compromise. IQ close to the same as the Canon and the 11-16, same build as the other Toki, wider range of focal lengths, 12mm is wide enough for me though it's noticeable difference with 10mm or even 8mm. Flare resistance I found good... second only to the Canon. I also like the constant aperture (and f4 is fast enuf for me). A variable aperture can be a pain if using manual flash or studio strobes, which I sometimes do (though not a whole lot with an UWA lens). Finally, I also found the price nice... a few years ago it was a bit cheaper than the $600 it's selling for now.
There is also the Tamron 10-24mm... It wasn't available when I was shopping, so I didn't get to compare it. It's the widest range of focal lengths in an UWA, and one of the cheaper usually under $500. I have heard it's a little soft at the 24mm end of the zoom, but check for yourself since I'm just passing along what I've heard.
I was able to compare another less expensive model, the Sigma 10-20 with variable aperture. It currently is right around $500 too. It was pretty good, but I didn't feel it handled flare nearly as well as the Tokina 12-24 and Canon. However, there is a newer version of this lens now, which might be improved.
There are actually three other Sigma options: 8-16mm, 10-20/3.5 and 12-24mm. I have not used any of these. The 8-16mm is the newest and the widest lens available, without going to the extremes of a fisheye. It does have pretty strong wide angle distortions, but that's not surprising. The 10-20/3.5 is also relatively new... it is the only other constant aperture UWA, besides the two Tokina. It also has HSM focus, which is Sigma's version of USM (so I suspect it would allow for FTM). It's a bit pricier but not the priciest, at $650. The 12-24mm is actually a full frame compatible lens, so is quite a bit pricier at $830 and somewhat wasted on a crop camera, but might interest someone using both formats. It also has fairly strong wide angle distortions, but that's not suprising in the widest lens on the market for a full frame camera. Currently it's a second version of this lens selling, but I don't know the details of how it was revised or what might have been improved.
Hope this helps... have fun shopping!