Financial statements for several years, tax returns, the list of assets and contracts transferring, payroll records, leases and licences. These documents both protect the purchase and supply the consulate with proof that the business is real and not marginal.
Diligence documents and visa documents are largely the same
A seller who hesitates to produce financial statements, payroll summaries and customer contracts is telling the buyer something, and is also depriving the E-2 file of its core evidence. Ask for at least three years of financial statements and tax filings, current payroll showing how many employees the business supports, equipment lists with ownership or lease documents, the premises lease and its assignability, and any licences the operation needs. Hypothetical example: a Boischatel buyer of a snow-removal and landscaping business asks for the municipal and commercial snow contracts by name, because assignable contracts are what make next winter's revenue real.
On the buyer's side, prepare the purchase agreement, escrow instructions, proof of Canadian citizenship, the ownership table after closing, a business plan with a five-year staffing projection, and the full source-of-funds trail. Translate Québec documents. The consulate will read the seller's paper to decide whether the enterprise can support more than the investor's own living.