It is possible but delicate. The enterprise-nationality requirement is met at exactly fifty per cent treaty-national ownership, assuming that ownership is genuine and remains at that level. Each Canadian investor holds only twenty-five per cent, however, so each must independently show development and direction through documented operational control; the equal overall split does not establish that control by itself.
Sitting on the line is not the same as being over it
Hypothetical example: the two contractors hold twenty-five per cent each and the American partner holds fifty, and everyone assumes an even split is fine. The nationality requirement is at least fifty per cent held by treaty nationals, so the arrangement is exactly at the threshold and every detail matters: how shares are recorded, whether any are held in trust for someone else, what unissued shares could do to the ratio, and what happens if one contractor sells. The control question is separate and equally live, because neither side can outvote the other.
Resolve it in a shareholders' agreement that allocates operational authority to the investors, and have that agreement reviewed before the company is incorporated. The other requirements still apply: funds irrevocably committed and at risk, a substantial amount in proportion to the enterprise, and a real operating business that is not marginal.