File when a clean continuous year abroad within the three-year window can be documented. If the earlier years provide that, there is no reason to wait; if they do not, waiting until twelve uninterrupted months have accrued after the leave is the safer course.
Let the calendar of employment, not the terminal's needs, set the filing date
Hypothetical example: a Rothesay logistics company's U.S. subsidiary has lost its terminal manager and wants the vice-president in place immediately. The petition date determines the three-year window, so the company should calculate, from a proposed filing date, which twelve-month periods within that window were spent continuously employed abroad.
If a period before the leave qualifies and still falls inside the window, filing now is sound. If the only qualifying periods are compromised by the leave or have slipped outside the window, the company should wait until she has completed twelve uninterrupted months after returning, and cover the terminal in the meantime through a local hire or a short business visit that involves no productive work. Filing early on a weak year risks a denial that delays the move further.
Once approved, she may be admitted at a port of entry without a visa stamp as a Canadian citizen.