Most Americans can freely visit Canada. However, if you have a criminal history, you may be refused entry. This post describes the circumstances in which a criminal record (including DUIs) will result in your being inadmissible even as a visitor, how long inadmissibility lasts, and what you can do to regain the right to travel freely to Canada.
Were you convicted?
If you were convicted of a crime in the United States or abroad, this will likely make you “criminally inadmissible.” Even if you were charged with an offence but never convicted, it is a good idea to travel with all your court documents demonstrating that there is no conviction on your record. Carrying all these documents, though not required, is highly recommended to avoid any confusion or refusals at the border as the onus is on the applicant to demonstrate that they are not inadmissible.
Border officers have the option to deny admission on grounds that it is reasonable to believe a person committed an act that would be an offence in Canada, so that pending charges may be grounds for a finding of inadmissibility. A guilty plea followed by dismissal of charges pursuant to a deferred adjudication scheme may also be considered proof of commission of an act.