with the current conditions Man United are better than Barcelona, but I still think that Barca could beat them in the 1st leg and It will be enough to qualify, keep in mind that the style of play is different and Man utd can find it difficult against Barca if they take control of the match.
Both of teams are in the best positions at this moment. I expect that MU must be facing a tough game against Barcelona. MU was at the top 3 while Barcelona was leading la liga this time. The performance from both of the teams in the local league were so good at this moment. MU needs to break its bad record against Barcelona. I hope that MU can do that. No reason for MU to lose against Barcelona. MU needs to surpass Barcelona and go go the next round of europa league.
Some clubs have been waiting for the result from play-offs like arsenal.