Here is something to ponder.
Let's say you were convicted of a DUI and are only flying into Canada without renting a car and just using public transportation because now one can't drive due to a disability? You now only have a State ID Card as opposed to a Drivers License hence you won't be driving and your relative entering with you is the one who will be driving.
Shouldn't they ask you questions such as I see you have a convicted DUI but will you be driving in Canada? If the answer is no then you can come in but if the answer is yes the Border Patrol can say either you cancel your rental car or prove that someone else will be operating the car and if you do not tell the truth you will be deported back to the USA.
I can see a person who was 70 at the time of the conviction now wanting to come into Canada at 74 but has no intention of driving.
I can see this as a problem because when you fly in who is to say you will drive. Now I think its OK if the rental car agencies did their own background check and after x amount of time will let you rent again.
But how can a DUI be enforced if you are flying into Canada and plan to take the train?
Just food for thought.