As soon as the corporate records and the role descriptions are assembled, which realistically takes several weeks. USCIS processing follows, shortened by premium processing where available. An empty seat should be covered by U.S. staff, not by the transferee on a visitor entry.
Fill the gap lawfully while the petition moves
Hypothetical example: the previous U.S. general manager resigned without notice and the siblings want the operations director in place next month. The petition cannot honestly be filed until the affiliate relationship is documented and the role descriptions are written, and USCIS then needs its processing time; premium processing, where available for the category, gives a decision within the service window after filing, unless a request for evidence pauses it.
In the meantime the U.S. company should appoint an acting manager from its own staff. The operations director may visit for meetings and to observe, but performing the general manager's duties on a visitor admission is unauthorized employment and endangers the petition.
Once approved, he presents the approval notice at a port of entry as a Canadian citizen. Sequence the family's move for the school term, and do not sell the Edenwold house before the approval notice exists. If the corporate structure needs a change to establish affiliation, add that time at the front.