Fly Boy, while not an Air Canada employee, I am aware of flight pairings that involve the employee dead heading the day before, to operate an early morning flight. I also know that many employees if possible do not wear their uniforms while dead heading (if they have the time they will change before / after the flight).

I am not aware of the requirements about drinking, but it would seem reasonable that if the employee was deadheading home they would be permitted to have a drink. I am aware though that they can NOT have a drink in uniform even if they are not working.