I have a 7D, it's a great camera, and especially good for video. You will love it underwater.
I have been using the Tokina 12-24 for a number of years now (I used to use it on my 10D), and it is terrific. Fast, good focusing, nice range and very sharp. Great for reef shots, big animals, wrecks and general video work. Other people have said good things about the Tokina 10-17 and the Canon 10-22.
The other lens that I use and enjoy is the Tamron 60 mm macro. I also have the Canon 100 mm macro, but the 60 mm is much better IMHO for macro work. The longer lens makes it harder to hold the shot due to the narrower angle of view, and I don't think that the fact that you can be a bit further from a subject has ever been an issue for me.
Better expect to buy two lenses, though... I don't think that you are going to find one lens that will be good for macro and wide angle...
Mike