I'd take a Canon over the Sealife cameras just about any time. One's a camera developed by one of the world's top imaging companies, the other, well, it just isn't. The Canons should be more versatile, especially if you are looking at one of their higher end point and shoots.
The G11 and S90 are very similar cameras, sharing many of the same internals (sensor, processor and such I believe). The G11 has a bit more zoom, probably a bit better lens, and a couple other things, the S90 is very compact.
I had a G9 that I really liked 'til it finally kicked the bucket this last fall, was looking to go to the S90 (due to the compact size) 'til I decided I'm really hot to trot for something with interchangeable lenses.
As Gabe mentions, you can take a lot of great photos without a strobe. The onboard flash works great for macro and anything within a couple of feet, shoot RAW and you can fix most other photos. I think on my blog I've got maybe 3 photos in the last 5 years using a strobe unit, (picked up an Ikelite AF-35 and used it twice, I don't care to carry anything that big in general) everything else was onboard flash or RAW and photoshop.