This is true that Barcelona have had several wins over Man United , but I do think that this time around it's going to be a different ball game, looking at Man United form and Changes over the years in both clubs. Barcelona had this incredible coach Guardiola and players, Lionel, Xavi, Iniesta and more compared to what they have now, basically a lot of things has changed which could affect the result too.
Without Xavi, Iniesta and other Barcelona's veteran players, they're able to beat Manchester United. Check the match on April 11, 2019 and April 17, 2019, only both Messi and Suarez playing as the strikers, the midfielders are same like the current year. It's really wrong to say Barcelona is really different with the old one, Messi is a GOAT, but football is a team play and the current Barcelona's players are good enough.
Even if Messi and Suarez are not playing I think that a goal machine like Lewandoswki is a great striker for any team to have and it is only natural for him to score a lot of goals because the other team members are making sure to serve him as many balls as possible during a game.I don't think he,Lewandowski will have that big of a problem to score against a team like Manchester United which lately has been conceding goals in almost every game they play,be it in the Premier League or other competitions.Barcelona is clearly the favorite in this encounter.