I would be quite willing to pay a change fee. I would be quite willing to pay the appropriate full fare and be refunded the lower fare. I don't even mind standing up all the way it is only a fifteen minute flight! No options exist.
This post was not intended to 'have a go' at Air Canada but a demonstration of how the 'service' element of flying today has disappeared especially among the bigger airlines.
If I make the crossing with Harbour Air on the seaplane they are totally flexible, they carry more passengers than AC on this route - no use this time though they do not fly at night. They will fly packages across, you can take excess baggage down on an earlier flight ( it is only an otter so space is limited) etc etc.
I ran a commuter airline, I also spent the best part of 25 years juggling charter flights their yields and contribution. In all cases reservations were able to look at individual cases and use there initiative. There was always a telephone number the passenger could call and talk to someone who had the power to at least look at the position sensibly, even if the answer was no.
Today so often there isn't.
I can see the difference between a small airline that carries thousands, not hundreds of thousands and the practicalities in that.
We have lost something along the way and as others have posted earlier nothing will change until it becomes intollerable.
I will let you know what happens 'on the day'.