Uprooting his family from Barcelona would always be a tough call esp. a young family and he doesn't have any roots in England as well. I read he has some properties in Paris and all. Plus an easy league win and pals with Neymar. So it would be an easy call and not a footballing one.
He ain't winning the CL with PSG. The league is not upto the mark and is highly derided among fans. Winning a PL and CL in England would mean he has done it all. He has clearly wasted some of his prime years in the drivel that is Barcelona so he may want to go out with a bang. Even if you remove City out of the picture, the reunion with Pep would be a great storyline.
And this goes without saying our club ,our manager our entire CFG project and the chance to win multiple trophies all of this should be a factor in his decision making. Imho Paris is an easy choice so is staying in Barcelona. The greatest of all time should go on a high and the probability of doing so is greater in Manchester than in Paris or Barcelona.
On a personal level I am not so invested in a 34 year old Messi. He comes, it makes up for a great news we get to see him play in skyblue and he may get us a couple more trophies than we could without him.
Signing Haaland and other players would mean trophies for the next decade. I prefer the latter or both :D