I put £50 on Barca, so yeah, that's my thoughts.
I don't think this United side are good enough defensively or on the counter to beat Barca at their best, on the other hand I don't think Barca have been playing particularly well for a long time, and in a one off game they're beatable.
Hope United get destroyed by Barca, then hope Barca get destroyed by that thing from Cloverfield.