I'm very surprised nobody has brought this up yet: many DUI charges these days are turned into "diversions" which are deferred adjudications cases. This means if you follow a prescribed alcohol rehab program (classes, fines, etc), after a year with no other bad behavior the charges are essentially dropped. The arrest record still exists and many airlines/military are now asking "have you ever been part of a pre-trial diversion or other deferred adjudication program?" These questions are designed to get to know you without disqualifying for you

The important part is that Canada won't know anything about it....