Just to be clear this has nothing to do with the Railroad. This is Canada not wanting someone who was recently arrested for DUI coming into their country. That makes perfect sense to me as I feel like DUI is still not taken serious enough in this country.
To the OP... Guess you should have thought about the consequences before drinking and driving.
'Cept in this country, we have a presumption of innocence- innocent until proven guilty... oh, Canada does, too. Adomonishing a person who has not been convicted that he or she should have thought about the consequences... well, that's patronizing. And useless.
I suspect Canada's issue here may actually be more subtle than a dislike of how the US handles DUI... the border agent, I'm speculating, was concerned about a person currently in the middle of criminal legal procedings in the United States perhaps fleeing to Canada.