I'd second everyone that said to use a Canon in a dedicated case.
They are rated for the depths that one would want (100+ ft.)
I have a Canon A650IS and mating case and cant complain about it.
(other than no HD video and Raw modes)
If you want a wide angle and HD video look at a
http://gopro.com/
Beforewarned, clicking on this link will make you want to do all sorts of cool things just because you have the camera.
Ross