Emergency exit row s can make a long flight bearable. Unfortunately, Air Canada does not allow these seats to be booked online, the agent at check-in has to make an assessment of your ability to hoist the door if necessary before assigning these seats.
Now, if the Air Canada booking system were to receive an assertion as to a passenger's size and strength from a trustworthy source, then the need for a visual once-over from the agent would disappear. If Dr Jones says you can lift the exit door, that would be good enough.
An advanced system could balance the plane based on weight, assign skinny people seats next to those with a tendency to spread beyond their allocated space, or put me right next to a chatty Grandmother with multiple photos of her family (oh wait that already happens).