In terms of applying for an E-2 visa, it is easier to buy an existing business than to start a new business. The reason is that the purchase price of the business is the investment amount. No other investment is required. For example, if a Canadian citizen purchases a hair salon in Los Angeles for $150,000, then the purchase agreement will constitute the E-2 investment.
On the other hand, to qualify for an E-2 visa by starting a new business the Canadian is required to invest the entire amount needed to get the business operational first.