I'm now believing in Manchester United they may succeed in defeating Barcelona. If Manchester United was able to defeat Manchester City in the premier league I don't see Barcelona to be that difficult for them. Manchester United is good to challenge any big team.
Maybe yes, maybe no.
Manchester City previously was lost to Southampton too, so we can say Manchester City performance doesn't really good recently. While Barcelona they have beat Real Madrid which is previous winner of Champions League, you need to know if Champions League is higher than Europa League.
I still think Barcelona has a slight advantage maybe 55-60% to win against Manchester United that either 40-45% to win.