Signed customer contracts, invoices and payments received, a lease or premises agreement, payroll for the existing staff and U.S. tax filings. A certificate of incorporation and a bank account with a single deposit from the parent do not establish that the entity is trading.
Show revenue, staff and premises, in that order
Doing business means the regular, systematic and continuous provision of goods or services; it is not satisfied by the mere presence of an agent or office. For a subsidiary with three technicians, the strongest evidence is a set of executed service contracts with U.S. customers, invoices issued against them and bank statements showing the payments arriving.
Add the lease for the shop or office, the payroll register and quarterly employment tax filings for the current staff, and the most recent federal return. If the subsidiary has been operating for less than a year, the petition becomes a new-office case with different evidence and a one-year initial approval, so establish the actual start of operations from the first invoice, not the incorporation date. The Canadian parent must also be shown to be trading, since the qualifying relationship requires both entities to be active, and a founder who has wound the Canadian business down to move south has undermined her own petition.