Registers and records rather than narratives. The two share registers, evidence that both companies trade, payroll showing the beneficiary's qualifying year, an organisation chart for the receiving company, and a duty description written by someone who knows what the role involves day to day.
Build the file from records that already exist
Start with ownership. Produce both share registers as they stand today, together with whatever created the current holdings, and be ready to explain any difference between the two companies' cap tables. Then prove activity: contracts, invoices, bank statements, a lease, business insurance and payroll for the receiving entity, and the equivalent for the Canadian company.
Employment comes next. The qualifying year is established from payroll records, records of employment and tax slips, not from a letter that says the beneficiary has worked there for years. Where there is a gap, leave or secondment inside the three-year window, address it in the file rather than hoping it is not noticed.
Finally, describe the position. An organisation chart naming subordinate positions, their salaries and their own reporting lines does more work than adjectives. If the receiving company will employ six people and four of them are installers, say so and explain how the role is still managerial, or consider whether a different category fits better.