Only if the completed purchase gives the Canadian company or its owners control of the U.S. plant so that they are parent and subsidiary or affiliates under common ownership. A partial stake without control, or a deal that has not closed, does not create the relationship.
Control is the fact that has to be visible in the closing binder
Start from the closing documents rather than from the business intention. If the Canadian company bought all the shares or membership interests, it is now the parent and the plant is its subsidiary. If the family shareholders bought the plant personally, the two companies may be affiliates because the same individuals own and control both in substantially the same proportions; the file must show that proportion with both share registers side by side.
A forty-percent stake does not by itself establish control, but a subsidiary relationship can exist below fifty percent if the owner proves actual control; a purchase into an entity controlled by an unrelated U.S. partner does not qualify unless the required common ownership and control are otherwise established. Both entities must also be doing business — regularly providing goods or services — for the whole period of the manager’s stay, so a Canadian mill that is wound down after the acquisition would end her eligibility.
Confirm the manager’s own year abroad was with the Canadian company and that her U.S. role will be primarily managerial. Fees for Form I-129 are on the G-1055 schedule.