The Fuji is probably a better camera for reef stuff than the powershot you're looking at. both are excellent cameras though, and you'd probably be quite happy with either.
The Rebel or 10D (different camera) are significantly higher quality than either, but they are much harder to get the same range of pictures out of without investment in one or more other lenses. (Macro in particular)
I've never used an S7000, but I've heard nothing but good things about them. It seems lately that the choice overall is Canon though, they are truly leaps and bounds ahead of the other camera companies for digital at the moment.