Do not assume the arrangement is authorized. Clarify the employer, activity and required process before relying on the proposed start date.
Treat the deadline as a planning fact
A commercial timetable cannot decide whether the actual employment fits the classification or current permission. Explain substantive changes honestly.
A Canadian citizen may request TN admission from an officer at a land port or airport preclearance location with proof of citizenship, the prearranged professional employment, and the required credential. If the employer, duties, or client assignment changes, request a fresh assessment rather than assuming the original plan still applies, and remember that a temporary TN offer does not remove the need to consider longer-term intent. Where restructuring is required, the limiting factor is usually a board or shareholder approval process with its own meeting calendar, so ask early when the next opportunity to approve a change falls.
If the engagement is expected to continue past it, start gathering the employer's updated letter and any refreshed evidence weeks ahead, since collecting documents from a different country on short notice is what most often causes a gap.