Ownership and control documents for both entities, plus current evidence that each is actually doing business. Registration alone establishes existence, not activity.
Two questions: who owns it, and is it running
Hypothetical example: The relationship evidence answers ownership and control: share registers, incorporation and organisational documents, and any agreements that determine who controls whom. That establishes parent, branch, subsidiary or affiliate status. The second question is separate and often thinner in the file.
Both entities must be doing business, which means regular, systematic and continuous provision of goods or services rather than the mere existence of an agent or an office. For the Canadian side that usually means current financial statements, payroll records, contracts and tax filings. For a new U.S.
entity the equivalent is the lease or premises evidence, the business plan, and the funding actually in place. A Selwyn firm should assemble both sets at the same time, because a strong ownership chain attached to a dormant entity does not satisfy the requirement.