The intercompany services agreement, payroll registers, tax slips and the share registers of every entity involved. Those documents establish who employed the manager and whether that employer qualifies.
Read the ownership chain from top to bottom
Begin with ownership, because it determines whether the question matters at all. Produce articles and share registers for the packing business, the management company and the new subsidiary, together with any trust deed or holding company instrument above them. Then produce the services agreement between the two Canadian entities, which should describe what the management company supplies and to whom.
Then the payroll: registers showing continuous full-time hours, tax slips naming the payer, and records of employment for any interruption. Add the manager's job descriptions as they stood in each period and an organizational chart contemporaneous with the year being relied on. Where the arrangement changed mid-year, produce the resolution or agreement that changed it.
The aim is a record an outside reader can follow without being told which parts to ignore.