I entered into a deferred prosecution for a DUI back in Dec. 2005. I completed my treatment and have had no other issues. I understand that i'm on probation until 2010 then my charge will be dismissed with law abiding behavior. I was planning on taking a train trip to Canada. What are the chances of me being denied entry. (Using a US passport for entry)
The border agent has the ultimate discretion to say who can and can't get in. In your case, any DUI within the last 5 years can keep you out. You must have a certificate of rehabilitation obtained from a Canadian Embassy inside the US or a temporary residence permit. The latter is easier to get. There are many excellent immigration attorneys in Seattle or you can try your luck with the Embassy or Consulate itself.