After decades of turning certain Americans away at the border and losing millions every year in hunting, fishing & other spending, on March 1st Canada changed policy to allow visitors with a single DUI or other misdemeanor as long as that did not result in imprisonment. This is for a "one-time" exemption from the long, costly process of obtaining a Temporary Residence Permit (TRP). This policy is at the discretion of the border officer, so be cool.
In the past, TRPs normally covered just one visit although exceptions existed. The new regulation also covers just one visit. Per the Minneapolis StarTribune, Doug Reynolds, executive director of Nature & Tourism Ontario, says the changes will help but he's hoping for broader, permanent changes. He says a permanent fix may be a year or two out.
To read the new policy: Operational Bulletin 389 - February*27, 2012
Crossing into Canada with a criminal record: Crossing the Canada/US Border - noto.ca