Payroll records, the employment contract, T4 or Relevé 1 slips and an employer letter for each entity, plus ownership documents showing that every employer in the chain belongs to the same group. Time with a company outside the group does not count.
Which document decides it
The document that settles the qualifying year is the payroll record read against the ownership chart. Hypothetical example: a Lévis marine-equipment manufacturer employed an engineering manager through a subsidiary for seven months, then moved him to the parent's payroll for the last nine. The three years before the petition contain more than one continuous year of employment, but only if both employers are proven to be in the same group; otherwise the officer sees seven months and nine months with two unrelated companies.
Assemble a one-page chronology listing each employer, its dates, its ownership link to the petitioner and the record that proves each entry. Add travel records if the person made U.S. trips during the year, because time spent working in the United States is generally excluded from the count.
A reorganisation, a name change or a merger during the period should be explained with the corporate document that caused it.