At our wedding day we got some unofficial paper from the marriage commissioner, and we got the "large" marriage certificate approx. one month later via snail mail. It looks like this (in BC) :
I think everyone receive this and this is the right form to send. There is a more detailed "Genealogy Certificate", but CIC doesn't ask for it. However, it happened more than once that CIC asked for something they already had.
Anyway, it's a good sign that they started to look into the January applications.