Personal identity and background documentation of the kind any United States immigration process requires, and clear records of where the money comes from. Follow the official programme's own instructions rather than a checklist prepared for another category, and route any payment only through the channels the programme identifies.
Prove the money and avoid intermediaries
Even where a framework does not impose the detailed lawful source analysis that the investment programme does, being able to show where a large payment came from protects the applicant in more than one place, including on the Canadian tax side and with the banks that move the funds. Keep the sale agreement, the account statements and the tax filings that explain it. On the personal side, expect the ordinary background and identity documentation.
On mechanics, be careful. A new programme with a high price attracts intermediaries who offer to handle payment, expedite the process or guarantee an outcome. No third party can guarantee a United States immigration result, and a payment routed through an intermediary is a payment that can be lost.
Use the official channels the programme names, keep the receipts, and treat any assurance that exceeds the official page as a reason to stop rather than a reason to hurry.