Kane is the better player, and also the better fit for United.
Spurs play similarly to United, and Kane has done brilliantly to make himself the Premier League's top scorer and top assister in that setup. Imagine what he could do at United.
Meanwhile, Haaland is scoring in a freeflowing Dortmund side. He's not facing the same opposition as Kane, nor is he playing in he playing in the same kind of team. Does Haaland have it in him to be a creative force when United face a low block in 70% of our games? Maybe, but it'd be a £150m gamble.
The thing that makes Kane so good is that he can play the centreforward position in various different ways: fox-in-the-box, target man, false nine. He'd be a manager's dream.