Yes, but with specific conditions.
Canadian ultralights carry no flight authority document, such as a Certificate of Airworthiness, and ultralight rules are quite different between nations. Flying across borders in an ultralight requires special permission. Since July 3, 2000 the pilot of a Canadian basic or advanced ultralight intending to fly to the U.S.A. needs to complete a Special Flight Authorization form and carry it with him/her while in the U.S.A. The authorization is good for 180 days. The pilot must also hold a Pilot Permit Recreational – Aeroplane or higher license. A Pilot Permit Ultralight – Aeroplane with a flight instructor endorsement and two hours cross-country experience also qualifies.