I had a seven hour delay at YYZ on a flight to LHR (at one point, I considered returning to YOW to take the late YOW-LHR flight) on July 18, for a three day trip.

AC provided a letter at the gate explaining the reason for the delay (74E had a radar failure; first backup was new 345, but no pilots available; finally loaded onto 763 after it arrived from LAX, was turned around, and crew arrived), and they offered 7500 points (took four weeks for the credit to show up). They also offered a meal voucher, but all the restaurants were closed.

Departed finally at 2:00 a.m. I arrived at 3:00 p.m. instead of 7:30 a.m. - 1 day of 2 in the UK wasted.

No free upgrade (I had already booked one, so they took my coupon) outbound or return.

Overall, I thought AC did a great job of keeping the passengers informed of what was happening, and welcomed the compensation they provided (compared to past performance).