Treat it as a proposed business date until the revised role and applicable process are assessed. An unchanged date on the offer does not establish immigration readiness. For a Canadian citizen, TN status generally can be requested at a port of entry without a visa stamp; alternatively, a U.S. employer may file Form I-129.
Resolve the substantive change before relying on travel plans
Record when the employer finalized the duties and when supporting evidence will be available. Confirm the steps that establish work authorization for the chosen procedure. An application, petition approval or admission can have different effects depending on the process and dates. Keep a contingency instead of assuming the earlier timetable remains feasible.
Work backward from a real start date, not a hoped-for border crossing. First obtain the final employer letter and credential evidence, then resolve translations or name discrepancies, and only then choose a direct admission request or an employer I-129 process. A request can be refused when the record is incomplete, so do not resign from current work or commit to relocation solely because a letter is drafted. Hypothetical example: a wind-turbine acoustics engineer is needed for a commissioning window, but the employer has not yet described the analytical duties. The sensible sequence is to finish the duty narrative, verify that the credential fits the selected profession, and set a fallback staffing plan if permission is not granted on the desired date. The project calendar is evidence of temporary need, but it does not waive the profession or document requirements. Keep travel arrangements changeable until the immigration step is resolved.