You actually have two beefs here:

• The lesser one is with Air Canada, who re-routed you as best as they could and should have resulted in getting you there 6 hours late, but at least the same day.
• The bigger one is with United who didn't try to re-route you due to weather problems and as a result you lost a further 10 hours resulting in a nasty flight arrival time at 4:00 the next morning.

As other posters have said, you'll probably get a 10-15% discount coupon from AC, but UA is typically more generous, so i'd get in touch with them and see what they have to offer you.