AA has their exit row eligibility policy online: aa.com/i18n/…exit_row_procedures.jsp . Obviously, Sunwing's policies may differ (indeed, different laws apply to a Canadian carrier), but it gives you an idea of what's meant by "eligible".
"Do you lack mobility, strength and dexterity in both arms, both hands and/or both legs to: quickly reach the exit, remove any obstructions, manipulate the exit door and slide mechanisms or lift out a window exit door, exit the aircraft, or assist others in exiting?" is the criteria that might be hard to meet with crutches.
While there's very little chance the exit will actually get used, if it does it'll suddenly be a rather crucial place to be. (Still, you don't have to take quite it as seriously as this fellow: theonion.com/articles/… .)