The decision whether to admit you to the US is discretionary on the part of the Customs and Border Protection Agent with whom you interact. This means that regardless of whether you have a criminal conviction, a Border Agent can deny your entry to the US for a variety of reasons.
That said, US Customs and Border Protection has clearly stated that a criminal conviction for impaired driving will not prevent a Canadian citizen from being allowed into the US. This is due to the fact that impaired driving is not considered to be a crime of moral turpitude. For more information on an impaired driving conviction and US travel, please consult the US Customs and Border Protection agency’s webpage: