It's unclear what the cause of the delay is. Maybe it is unscheduled maintenance but I'd push Air Canada further to get specifics. Certainly under the APPR they must provide compensation for scheduled maintenance and unscheduled maintenance that was caused due to negligence (i.e. forgetting to leave the heating on in an aircraft overnight causing pipes to burst). At the same time, you cannot simply look at the root cause and stop your analysis there. You have to look at all causes of the disruptions and determine the role they play on the disruption. For instance, if Air Canada did not rebook you on one of their flights departing within 9 hours of the originally scheduled departure time and did not rebook you on the next available flight of any airline (including competitors) an argument could be made that the cause of much of the disruption was a commercial decision made by the airline to reduce the out of pocket costs associated with having to rebook you on a competitor airline which would be eligible for compensation.

-RooFlyer88