I was also using G10 as my second camera until this Jan, when the housing showed signs of possible leak. I decided to switch to G1x mark 2. The other cams I considered were Pana GH4 and Sony Rx100 III or IV. But the latter two require expensive Nauticam housings. With Canon, I can use the much cheaper Canon housing. The only down side I see is that the G1x II does not have 4K video. Haven't tried it under water yet, but happy with it so far as a carry along camera.
I was also looking at G7x, but decided to go with G1x II under the assumption that bigger is better (sensor).