Both Manchester United and City need wingers, and Mitoma will be fit in both clubs, just that the player will be the one to decide which club he will prefer to join in the January transfer window, that is, if Brighton will be willing to let him leave in the transfer window.
Rather than looking for a new winger, it's better for Manchester United to sign a new goalkeeper and few defenders. Their midfielder and striker already strong enough, so they just wasting their money to sign a new winger.
A player will join a big and tough team, Manchester United only a big team, so Mitoma should be in Manchester City.
This is correct, Manchester United failed to invest in ball passing defenders and the ones that are barely booked in both big games and small games.
Investment in a new goalkeeper would not be part of the plan for the upcoming transfer window. Before plans to get a new winger, they have to let go of both Martial, Pellistri and if possible the name Amad Diallo.
Mitoma is a very direct winger, though Manchester United can's get him because they have a future for that right wing with the name Garnacho. Mitoma to Manchester City would also not work, they have both Jack Grealish and the Belgian International ( Doku )