Canadian nationality of the applicant and of at least half the enterprise's ownership; a substantial investment irrevocably committed and at risk in a real, operating, non-marginal business; and that the applicant will develop and direct it. Canada is a treaty country, so nationality is satisfied by citizenship, not permanent residence.
Nationality, commitment, substantiality, marginality and control
Five conditions decide the case, and a marina purchase touches each. Nationality: both spouses are Canadian citizens and will own the marina, so the enterprise carries treaty nationality; if a U.S. partner took a majority stake, that would change.
Commitment: funds must be committed and at risk, satisfied by a completed purchase or an escrow releasing only on visa issuance. Substantiality: the price of the marina compared with the cost of acquiring it, which a full purchase satisfies. Marginality: the business must be able to generate more than the couple's own living, shown by existing staff and revenue and a plan for more.
Control: the principal applicant must own at least half or hold operational control. Beyond these, E-2 is not a path to permanent residence and must be renewed; the couple should treat it as a way to run the marina, not a way to immigrate. The consulate, not USCIS, normally decides a Canadian's E-2 visa.