This is not necessarily directly related, but the United States has a right to determine who is admissible to their country, and not having a criminal record is one of their criteria for admitting somebody into the United States. The age of the offence is not relevant: you have a criminal record. And the United States also does not recognize Canadian pardons. In that situation with a commercial truck driver, he or she is going to be detained.
On May 6th, 2008. See this statement in context.