A single uncomplicated DUI over ten years ago with no subsequent legal problems OF ANY KIND is usually just a mass of paperwork but nonetheless can be done by a highly motivated individual him/her self.
Anything more recent or more complicated, and you are probably going to need professional help:
Canada Immigration Lawyer for Canadian DWI Entry
An excerpt:
The eligibility criteria for Criminal Rehabilitation by virtue of time is very simple. A person may be eligible to be "deemed rehabilitated" if they have only one conviction, all jail time has been completed and fees and fines have been paid at least ten years prior, and the offense is not considered a serious crime in Canada (such as a felony) and did not involve a weapon or physical harm/property damage. The eligibility criteria for Streamlined Rehabilitation is also very simple. A person is eligible to apply for CR if all jail time, restitution, and parole or probation have been completed for at least five years. You can not apply for streamlined Criminal Rehabilitation at a Canadian Port of Entry like you can with a Temporary Resident Permit. The application process involves a large number of documents including photocopies of a United States passport or birth certificate, photo identification, a copy of court documents for each conviction as well as proof that the sentences have been fully satisfied, Police certifications from the state where the convictions happened and from any state you have lived in for more than six months in the past ten years, and lastly an FBI identification record. It costs 155 American dollars to apply for Streamlined Rehabilitation, but the Deemed Rehabilitation process is free. Because the application process is very complex and requires you to obtain several legal documents, retaining the services of a Canadian immigration lawyer is highly recommended. An attorney experienced in Canadian immigration matters will be able to ensure the application is submitted accurately and completely, which can maximize your chances of successful entry to Canada.