Work backwards from the credential and citizenship documents, which are the slow items. The request itself is comparatively quick, but it cannot be made before those records exist.
The slow items are institutional, not governmental
A seasonal agronomy start date creates a hard deadline, and the schedule is usually set by institutions rather than by the government. A registrar's certified transcript, a replacement citizenship certificate or a foreign credential evaluation can each take weeks, and none of them can be compressed by urgency.
Canadians are not issued a visa stamp for this category, so the request is presented at a port of entry or made through an employer's petition, and the choice between those two routes has its own timing consequences that should be settled early rather than at the last moment. Build the calendar from the longest lead item, confirm the employer can support the requested period, and leave room for a document that arrives with the wrong name or the wrong date on it.