The B-1 After Sales and Service category under NAFTA allows a Canadian or Mexican citizen to enter the U.S. to perform limited work without requiring a work permit.
Mexican citizens must apply for a B-1 Visa Stamp at a U.S. Consulate. Canadian citizens do not require a B-1 visa to enter the U.S. as Canadian citizens are considered “visa exempt.” A Canadian may enter the U.S. as a B-1 visitor using a passport or NEXUS card and presenting himself or herself for inspection and admission. Documentation outlining your eligibility under After Sales and Service should be submitted to the CBP Officer at each entry.
B-1 Business Visitors are usually admitted to the U.S. for 6 months at a time. The length of stay may be shortened due at the discretion of the CBP Officer due to factors such as number of previous entries to the U.S. or the length of the anticipated activity/event.