If the flight were originally delayed due to mechanical issues, then I would not even bother submitting at all. Mechanical issues = safety = no comp. That was your original flight, that is the reason the original flight did not leave on time, and then they eventually got you to your destination after they delayed the original flight for safety. I see no real way to get any comp here.

For the record, I have had one successful claim with AC (EU261, not the Canadian). The year the 787 was introduced, I got involuntarily downgraded from PY to Y because the 787 was late being delivered to AC and they had no other planes with PY. They downgraded my ticket to flex in Y, offering $0 back, no refund, and nothing else. I spent 5+ hours on the phone trying to resolve it with them, they refused to budge. So I took the flight with the flex ticket in Y and submitted under EU261 and successfully get compensation. I got a 75% of the total r/t ticket back in cash or 100% of the total r/t ticket in AC gift Cards.