I know quite a lot can change over a span of time, but in 2002 the process for Rehabilitation and Expungement of Criminal History  for a DWI was not too bad.  It was around $200, and the form to be filled out apparently was the same for a DWI as it was for Axe Murderers, Child Molesters and Bank Robbers.  Without my being aware, they had recently closed the Customs House at Prairie Portage and for the first time I had to obtain an RABC to enter there.  The trip date was not far off so I made a call to Thunder Bay and talked with a very helpful individual who explained the process.  As I remember it only took  two or three months.  Although the form is one size fits all, I would guess non-violent and offenses where there is no actual victim, committed in the USA, are dealt with more easily than other onerous issues.   I have to wonder if a person applies for Rehabilitation if that automatically slots you in their system as Inadmissible  until your paperwork clears?    The Temporary Residency Permit mentioned is intended to be for emergencies, work, death in the families, etc., so no guarantees here either.