Obtain the engagement letter and the licence standing letter first, then apply at a port of entry a few days before the start date rather than filing an I-129, which takes longer. Do not begin any U.S. fieldwork or client meetings that amount to work before admission.
Port of entry first, petition only if there is time
For a Canadian citizen, applying at a port of entry avoids waiting for advance petition adjudication. Once the U.S. firm's letter is final and the regulator's standing letter is in hand, the surveyor can present the package at a land or airport port of entry and, if admitted, start on the agreed date. Filing Form I-129 is an alternative if the firm wants USCIS review before travel; current processing times should be checked, and premium processing may be available. What should not happen in those five weeks is preparatory fieldwork on the U.S. side in visitor status; scoping meetings may be permissible business-visitor activity, but running a survey crew is not. If the letter is still being negotiated, push the start date rather than presenting a draft.
Hypothetical example: a boundary-survey specialist has a signed assignment beginning after a planned utility outage, but the standing letter from the regulator expires before departure. Renew the standing evidence first, then confirm the U.S. letter still gives a future start date and clear duties. The complete package, rather than the calendar alone, determines whether a direct admission request is sensible. If the employer elects the petition route, obtain the approval before scheduling productive work. A common timing error is crossing as a visitor to attend what is described as an orientation and then beginning measurements or directing a crew. Keep any pre-entry activity limited to lawful planning, and record the first day of professional services only after the proper admission is granted. If a material project detail changes, use an updated letter rather than explaining around an obsolete one.