It really depends on a few things in reality - primarily, your budget, and how certain you are that you're going to upgrade to full frame. The latter is the less important -- if you find yourself needing a wider lens, it's not worth it to wait until you buy a new camera, even if that new camera has the potential to not be compatible with the lens you buy (if you buy used, you can resell for about the same price once you switch to full frame, for example, and effectively end up with a relatively cheaply rented wide angle solution).
Firstly, you aren't exactly 'handcuffed' by your 7D. You can get a great wide angle lens like a 10-22 f/2.8, but if you're sure you're going to be upgrading (wish I had known about this, I would have cut you a sweet deal on my 5D2), then as you mentioned, you'll want to get into something that's suitable for full frame, etc.
I don't personally have experience with the Tokina 16-28, but I do hear about quite a few people buying/selling them and know of a few people that have owned it and said some pretty good stuff about it. That said, I have to agree with you that the build quality of Canon L glass is usually pretty superior.
I don't know how you feel about purchasing used gear, etc, but KEH has a couple in stock at the moment - used for $1269.99 in Ex+ (which will basically be like new), but also they have some EX+/LN Ver. 1 copies of the lens for much less (closer to $1070). That might be something to consider, given that the price of the Tokina BNIB is ~$850 from what I can see.