Thanks to all for the responses and great info. Really appreciate it.
We did visit San Diego 4 or 5 years ago (great city!) -- so we're trying LA + Palm Springs this year as we've never been there.
I am aware that the weather in the OC in late December is not perfect, but we are okay with any place that is warmer than Ottawa. (I'm sure you all know... it'll be about -25 deg C here at that time of year.)