Start assembling evidence at least a season early and file as soon as the employment year and the affiliate relationship are both in place. Add premium processing if the crop calendar leaves no room, and plan for a request for evidence rather than assuming a clean approval.
Work back from the crop calendar, then add a margin
A transfer meant to fix a production problem before a specific planting window has to be scheduled around USCIS, not the other way round. Regular processing for Form I-129 varies by service center and season, and a request for evidence, if issued, adds time for the response and renewed review. Premium processing guarantees action within the service window but that action may itself be a request rather than a decision.
The prudent sequence is to confirm the grower's continuous year abroad and the affiliate's active status, gather the technical exhibits while the current season's reports are fresh, file with premium processing, and hold the travel and housing arrangements until the approval notice arrives. Because Canadians present the approval at the port of entry rather than applying for a visa stamp, the last step is fast. If the season cannot wait for any of this, the affiliate should plan for local hiring as the interim answer rather than sending the grower to work without status.