Both are around the same price, and both have inexpensive housings. Both have 720p video, 10+ Megapixel sensors, etc. etc. They're largely the comparable as far as specs.
The main things that seem to differentiate the Sony WX-1/B is the ability to do a 10 fps "burst shot" and "bracket shooting" in which the camera takes 3 rapid shots using 3 different exposure settings.
Generally I hear more good things about the Canon sensor as far as low-light performance. Whichever camera will produce less grainy pictures in low light is what I'd like to go with.
[NOTE: I do not intend to use an external strobe and I am freediving in Southern California, mostly in the kelp. I will most likely only use the camera during decent viz in 0-30ft.]
Any suggestions are much appreciated!
Cheers,
Dave