If you have the canon WP-DC50 for your A95 I think I'm right in saying that your only option is an Inon lens.
The problem with the front of the Canon housing is that you need a specific lens adaptor to hold a wide lens. Inon make such an adaptor and I pretty sure no one else does.
Both the Inon AD UWL105 and AD UFL165 are possibilities. If this is your first wide lens I would recommend starting with the 105 lens which gives about 100 degrees coverage on this camera.
A word of caution though. I experimented a lot with this set up and found a modified version on the AD-DC700 adaptor sold for the canon A70 worked better than the one specifically designed for the A95. The correct adaptor appeared to result in vignetting problem as the lens is held too far away from the front housing port.
If you can, try one on the camera before buying to see if you agree with my findings.
I can always reply again if my suggestions are of further interest
Trevor