This is really interesting, as I have been looking at these two cameras along with many others here.
I will look forward to your experience, Freewillow, I hope that you will let us know how the camera works for you.
Firstly, while the Canon S series came up, it was not by the OP, so I won't comment, other than it is out of the running for me due to the battery limits, if I was down for two dives or more, I would be running on empty and swapping batteries in wet places - no good.
Last year there were a few threads that seemed to suggest the expert opinion was that the Sony wins every which way on Video, so that seems to be settled. Comparing the Rx and the G in Macro was less clear; the Sony wins, but with the use of diopters and strobes (1 or 2, with trays etc) and so was better for those with more cash on hand, and those traveling with first class baggage allowance, and all that goes along with bigger Kit (chargers, etc.). As for general wide angle, I can not comment or remember, but I would assume the Sony performs as well as the Canon and the pixels would be greater.
Other thoughts include the fact that Sony housings can be quite a bit cheaper than the Canon ones - why? because they are smaller? and need to compete with the S series housings? Seems a bit lame to me, but that was the case last December when I looked. so that tightens the 'raw' camera purchase a bit - Sony +1. There are other cost issues, like the missing charger with the Sony - Sony -1, but that is all covered elsewhere.
Topside, the Sony really shines, but one thing really kills me... No finger grip! I carry my camera in hand a lot, and in warm climates, with a bit of moisture, this camera would be hitting the ground. If you look at cheaper Sony's, they have the grips, and if you look at the $2500 re-badged more expensive versions of this exact Sony model, they have them (in Rosewood!) - so why not on this model? Sure, you can 'stick' one on, but then it won't fit in your U/W housing - or so I was told. And along with that issue also goes the un-protected Video Hot Button, not great.
But I wanted to love this new Sony, and because I mostly love macro, I did 3 test sets in 3 shops around town. side by side hand held Macro(ish) shots at the counter. I used old circuit boards and LEDs for color tests.
My thought was, with the additional pixels, the macro spread between the Sony and the Canon may appear less - by cropping down the larger Sony image taken from further back. I shot with and without flash, and held the Canon back 1.25", as to be fair, while as it can focus closer, not in macro mode while INSIDE a U/W housing, as in Macro the Canon is fully back from the glass about 1.25". The tests did not use additional Strobes or whatnot as I just don't want to travel with so much equipment. I look forward to smaller U/W lighting units in the (bright) future...
In short, the Canon images won the day in sharpness (in my opinion), mostly due to close macro focus limits with the Sony. The Sony colors were richer, almost syrupy after the Canon, but I could get to like that. But for me, and in the crunch, I need the sharpest image I can get, without additional lighting. Can one get sufficient light for the Sony's macro(ish) down past 45 feet without clear 12o'clock clear sunshine - I worry that, no, it is not likely.
I do look forward to tipping into the Sony Snappers forum, but I'm not there yet. Maybe with the rx3?