As a general rule, Canada does not allow persons with DUI's to enter their country, although travellers who require in-depth information regarding the process of applying for a waiver or other admissibility questions can reach the Canada Border Services Agency (CBSA) during regular business hours, Monday to Friday (08:00 - 16:00 local time, except holidays) by calling either (506)636-5064 or (204)983-3500.
You may also view the following links with CBSA on their waiver process:
• Citizenship & Immigration (for related policies and procedures on waivers): http://www.cic.gc.ca/
• CBSA’s home page: http://cbsa-asfc.gc.ca/menu-eng.html
• CBSA’s Contact page: http://cbsa-asfc.gc.ca/contact/bis-sif-eng.html
• CBSA’s info for non-Canadians: http://cbsa-asfc.gc.ca/noncan-eng.html
A single DUI conviction is not grounds to deny entry into the U.S; however, multiple DUI convictions or a DUI conviction in combination with other misdemeanor offenses can make a person inadmissible and require a waiver prior to entering the United States.