After the qualifying relationship genuinely exists, not before. The relationship must be in place at filing, so a petition submitted while the purchase is still conditional invites refusal. Against that, the seven-year ceiling for this category is cumulative, and time already spent in American status counts toward it.
File behind the closing and ahead of the ceiling
Hypothetical example: Thibault already worked five months inside the United States on secondment before the group settled on transferring him. Two clocks run in opposite directions. The first says wait: the ownership must be real and provable on the filing date, both companies must be doing business, and an American entity that has traded for less than a year is treated under the new-office rules with a shorter initial approval and an extension that has to be earned.
The second says do not dawdle: this category permits a maximum of seven years, Thibault's five months of American secondment may already count against that total depending on the status he held, and the group's plan to keep him in place for the first years should be checked against what remains rather than against a blank slate. In between sits the practical sequencing question of who employs him during the interval. Remaining on the Canadian payroll, directing the transition from Quebec, keeps the record clean until the petition is decided.