Great news!! The tourism facilitation plan has been put into effect as of march 2012 making it easier for those with 1 minor criminal infraction including dwi's regardless of how long ago.
If a person has 1 and no more criminal infractions with less than 6 months sentence they are eligable to recieve a 1 time admittanace into canada with no fee.
It must be done at the border and is discretionary however if 1 and only one infraction the border crossing personal are discretionarily directed by the policy.
It does not change the basic laws,it is meant to to help those expereince canada who have only 1 infraction and are staying at a tourism facility and thus pose no threat to repeat while on thier vacation.
to get a permanant rehabilitation you still must first wait the the min. 5 yrs to apply and will be instructed as to how to apply upon recieving the 1 time permit.
The immingration personal i talked with suggested it always helps when coming to bring a copy of your criminal record and several references indicating the infraction was a 1 time thing and out of character.
also see sticky post "border crossing info for more