Not sure about Barcelona and PSG will be there until the final stage, especially about Barcelona which seems like Barcelona's performance will still not be much different from the results they got in the previous season too. But for Manchester City, of course I personally still believe Pep Guardiola still has a very good ability to make Manchester City go further. Also about Manchester United, although the chance to get the title is very low but at least Manchester United has a good chance to get to the quarter-finals, maybe.
Current performance from Barcelona is not impressive in UEFA Champion League after failure in group stage last two season, I don't think with promising performance from Xavi Hernandez teams next season due will get bigger or competitive teams in group stage drawing. Still has possibility for Barcelona in the same group with Bayern Munich, its difficult for Barcelona qualifying in group stage after last season loss in home and away match against Bayern.
Although have been confidence performance as La Liga winner last season, seems not enough thing how diffiucult faced by Barcelona qualifying from group stage. PSG is not in my favorite teams list for winning UEFA Champion League next season, losing Lionel Messi and not clear yet with Mbappe future is strong reason PSG is the weakness teams in for winning UCL tittle.
Maybe yes it is unlikely that Barcelona will reach to the final UCL, Xavi is still has not been able to bring Barcelona to good play in this big caste in my opinion he still loses his tactics against big clubs in europa, although on the other side the Barcelona squad looks good. Indeed, PSG current situation not good, losing Lionel Messi and not clear yet with Mbappe next season, to be honest I personally also doubt it although this big event is full of surprises.