The investor, and the owners of at least fifty percent of the American enterprise. Nationality is traced through holding companies to individuals, so a corporate shareholder carries no nationality of its own; an exact fifty-fifty split with an American co-owner still meets the ownership threshold, while anything below half does not.
Follow the ownership until it reaches people
Hypothetical example: Mireille runs a boat sales and service business in East Ferris and plans to buy a dockside repair operation in the United States with two co-investors: her sister, a Canadian citizen, and a long-standing supplier who is American. The shares as drafted are split evenly in thirds, which puts Canadian ownership around sixty-seven percent and clears the fifty percent threshold — but only if the register says what the plan says. Two things commonly break it.
Ownership held through a numbered company has to be traced to the individuals behind that company, since a corporation has no treaty nationality of its own. And a shareholders' agreement giving the American partner a veto or disproportionate control can undermine the finding that Mireille develops and directs the enterprise, even where the percentages look right. Resolve the register, the agreement and each shareholder's citizenship documents before the closing date, because restructuring afterwards is expensive and looks contrived.