The Swans lost 1-0 to United on the weekend.
But Gower warned: "United have got good rotation in their squad, but at times they have too many players who drop off. It makes them difficult to pick up and allows them possession.
"But you obviously prefer someone like Rooney playing deep against you. The last thing you want is for him to keep getting in behind your back four and running in on goal.
"If you can keep him in front of you then he's going to have to produce a helluva strike to beat you."