Can some1 with a pardon in Canada travel to the US if never tried to cross with convictions on their record b4?

MY cousin had a record up until last year in Canada and he only tried to cross the border when the charges were laid, but he was not convicted at the time. That was before 9/11 and he hasn't tried to cross with or without his record. Does he need a waiver or will nothing come up in the system? Thanks!