For those of you who don't know this camera/housing system, it would suit an underwater photographer who is keen to shoot in TTL mode, or a wedding photographer who likes working in really wet conditions.
Its main drawback is an inability to use Canon lenses.
Its main drawback is an inability to use Canon lenses.
Its main advantage is the ability to use Nikon lenses
Seriously, the Nikon system has the advantage in underwater photography in that Nikon has more wide angle lenses available--a key to underwater work especially when trying to combat the 1.5x crop factor. There is no Canon analouge to the 12-24mm or the 10.5mm. The Sigma 12-24mm is currently not supported in any housing--a fact that will certainly change in the future, however the quality of the Nikon lens is superior to the Sigma. The only advantage to the Canon system is price and telephoto and telephoto isn't useful underwwater. Of course if you already have Canon glass, Canon wins hands down.
In truth the TTL of the S2pro is the biggest advantage, Nikon glass is only the second biggest advantage.