I just tried to book some reward flights using my OnePass miles on the CO website and noticed that:

-the CO website for bookings is fast and easy to use;
-taxes/fees for reward travel on CO.com are calculated directly during the booking process without having to call in to a customer service representative; for the same flights that I was searching for on aeroplan.com, I had to call customer service to calculate the taxes/fees manually;
-availability for SQ operated flights does not seem to appear on Co.com, but were available on aeroplan.com (example was PEK-SIN-PEK where only Air China operated flights were shown on CO.com but SQ operated flights were also shown on aeroplan.com)