You now need to apply for a U.S. Entry Waiver in addition to the Pardon. Do not try to cross the border again until you have obtained one, as you could be detained and/or banned from re-entering the U.S. for a period of two to twenty years.
Pardons Canada undertakes all necessary steps and procedures for removing your criminal record, including: Pardons/Record Suspensions, Purges, Photograph & Fingerprint Destruction, and U.S. Entry Waivers.