You can also book seats online - so long as you pay an extra £10 per flight. The seatbooking on the website is notoriously suspect. You may have paid extra to book seats in advance, but the website will often refuse to take the reservation, once it has your money. Accordingly you may be better off saving your money, and then just calling up Air Canada to reserve seats.
Most cheap economy tickets are non-refundable and non-transferable, however you can often make a change to flight time or day, which, oddly, halves in price to just £44 on the day of departure. This can be a lot cheaper than a flexible ticket.
Be warned that when you make an Ebooking booking and enter any other FF number than an Air Canada number, often the booking will default back to an Air Canada FF number. Check your boarding card to make sure it has been correctly entered.
Air Canada 767 at Toronto, bound for London LHR|
To start with, make sure you are a frequent flyer, and you do fly frequently: after all, if Air Canada are going to upgrade anyone, they will upgrade those passengers who fly with them pretty regularly, and hence will enjoy the upgrade enough to put more business Canada's way. Then if the flight is full in economy, and someone needs to be moved up, the check in staff will first look at Aeroplane SuperElite members, and then Aeroplane Elite level, and then at other Star Alliance members at the equivalent levels (Gold, then Silver).
Another thing that Canada look at is how much you paid for your ticket: it's much more likely to happen with a full fare ticket (although occasionally you can get lucky with a discounted economy ticket). On Canada the airline has heard - probably hundreds of times a day - requests for an upgrade: the general consensus seems to be that if you ask for an upgrade, you're much more likely to get it: there are no points to be gained by being shy. Although opinions differ on an upgrade strategy for Air Canada.
As always, my advice on dressing properly in the pages on how to get an upgrade applies.