I think Barcelona will win against Manchester United and now that Cristiano left for the stubbornness of Ten Haag,the coach who wanted to make himself famous by not making Cristiano play (but history will remember Cristiano and no one will remember Ten Haag) is not going to be a big threat to Barcelona now,their attack lacks compared to that of Barcelona which has Lewandowski which is a true goal machine.
Manchester winning against Burnley does not show anything good from them as Burnley plays a category below Premier League and despite leading that category it has conceded goals in most of their games.Now I can bet easily on Barcelona to qualify further and I am sure I will win my bet.
Even if christaino Ronaldo is still in Manchester United I don't think if it will make any difference, because before he left the club he was not playing for Manchester United frequently, I can't say christiano Ronaldo is the reason for Manchester United wins in this season. If Manchester United and Barcelona should meet I know it won't be easy because this teams are big teams and they both have quality players. The game will be tough, but Barcelona may likely win the game.