I didn't receive a letter, it might still come as this flight was the week before Christmas, just saw the credit on my Aeroplan account with the description:
AC JAZZ FLIGHT DISRUPTION 3 HOURS - 4000 miles.

There was no financial compensation except a $ 15.00 food coupon which was very helpful, though there wasn't much to get at Kamloops airport.
Some people took bottles of water and juices and others candy bars to make up those $ 15.00.

As mentioned in the original post it was handled very well, nothing like what happened in Berlin on BA, we were all on the plane DASH 8 for about 1/2 hour when they found out that the cargo door couldn't be closed. They send mechanics with the next flight in, 3 hours later and actually came in on a Canadair Jet instead of the DASH 8, with 50 seats instead of the 37 of the DASH 8 they flew us all back in a jet.
The DASH 8 was repaired and came back almost empty that same night.