The signed joint-venture or operating agreement with its governance provisions, the U.S. entity's formation documents and ownership register, board or manager appointments, and bank-account signing authority. Together they should show equal representation and mutual veto over major decisions.
Governance documents carry the point, not a cover letter
USCIS reads control from documents, not from a description of the parties' intentions. For the Harrison Hot Springs spa venture, assemble the operating agreement or shareholders' agreement in full, with the sections on voting, board composition, reserved matters requiring both parties' consent, deadlock provisions and the appointment of officers. Add the U.S.
entity's certificate of formation, its ownership ledger showing the fifty-fifty split, resolutions appointing the Canadian company's nominees, and the bank's signing-authority form. Include the Canadian company's own incorporation and share records so the chain from the Canadian shareholders to the U.S. entity is visible.
If capital contributions differ from the ownership split, explain why, because unequal contributions with equal ownership invite questions. Then add the ordinary L-1A exhibits: the manager's payroll and appointment records for the qualifying year, the organizational charts for both operations, the lease for the U.S. premises, the business plan and financial statements.
A short index mapping each regulatory element to its exhibit makes the file easier to adjudicate.