Well according to the Guardian he is more interested in joining a traditional big club like Madrid, Barcelona, United etc rather than City, PSG, Chelsea
If that's true and Real/Barca don't show proper interest in him then he could probably be convinced to join United. He's won 4 Serie A in a row at Juventus and a new challenge might appeal to him now also
Barca doesn't have the kind of money been mentioned in regards to Pogba