A proposed start date does not resolve an unsettled professional assignment or confer work permission.
Resolve the assignment before relying on it
Confirm the actual engagement and use the appropriate immigration process. If the employer changes the role during preparation, reassess the case rather than submit a description known to be outdated.
Do not let the payroll date outrun the immigration facts. Before travel or productive activity, obtain the final duty allocation, confirm the US or foreign employer, the U.S. entity for which the activity will be performed, and the temporary engagement, and match the work to one listed USMCA profession and its qualification rule. TN is available to Canadian or Mexican citizens, not merely Canadian permanent residents, and it cannot be used for US self-employment. Have the employer date each revision and issue a current support letter. A Canadian may generally seek TN admission at a port of entry or rely on an employer-filed Form I-129; neither route makes work lawful before the required approval or admission. The recurring mistake is treating onboarding, orientation, or remote system access as harmless when it is productive US work.
Hypothetical example: A Saint-Ambroise civil engineer is scheduled to begin while human resources is choosing between design review and construction coordination duties. She postpones US work, obtains the approved allocation, and checks whether the final activity fits the profession supported by her engineering degree. When the employer removes a sales responsibility, it dates the revision and explains the change. Her start is then coordinated with the selected TN procedure, not the internal scheduling target.