I just did a search and found a listing saying that ca is a popular abbreviation for casa. If that's true in this case, I would think it is pronounced as KAH.
Now for a related question, how about the pronunciation of Opus X? "Opus ex", "Opus ten", "Opus diez" (like cinco vegas)? I always take the easy way out and just call them "Opus". But then there's the XXX which could be "triple-x", "ex ex ex", "thirty", "treinta", "tres equis" (hope not, I'm not a dos equis fan).
Geez, I'm thinking way too much here. I think I better just go outside and have a smoke!
-Lenny