There is no fixed minimum. Substantiality is measured against the total cost of purchasing the business, and the investor's committed funds must be a large enough share of that cost to show serious commitment and a realistic chance of running it successfully.
Substantial is a proportion, not a price tag
The consular guidance uses a proportionality test: the lower the total cost of the enterprise, the higher the proportion of that cost the investor is expected to have committed. A dealership with a purchase price, working capital and initial inventory requirement of several hundred thousand dollars would generally expect the buyer to have committed most of that amount, whereas a very large business can qualify with a smaller proportion. Borrowed money can count if it is secured on the buyer's personal assets, such as a mortgage on their South Frontenac property, but a loan secured only on the dealership's own assets does not show the investor's money at risk.
Separate the investment figure from the costs of applying: the consular application fee, professional fees, business valuation and the accountant's review are expenses, not investment. Verify current government fees from official sources at the time of applying. Keep a schedule that shows the total cost of the enterprise, the committed funds, their source and the proportion, because that schedule is what the officer will test.