Have you tried Travelocity Empress? I just checked and it gave me an OK on CP993 on Sat and 976 on Monday for the 378 NGETAWAY fare. Other flights may be truly full. Even AC has been oversold on many flights I was on in the last month.

I let it find the best itineraries on Travelocity just to see if there were any routings that would work on that fare.