I honestly had a bit of hope to see Man Utd in the final but after seeing the way they have been playing lately in the Premier League I feel like it is too much, even reaching the quarter finals I am still skeptical, the same goes for Tottenham. Both teams are playing very badly, I don't know what the problem is, but one thing I am sure of from Man Utd's slump is that they don't have a reliable attacking player, while Tottenham under manager Ange their quality has declined.
Another option I would like to see is Bilbao, I think they can reach the final.
It is also very natural for you to be skeptical about Manchester United and also Tottenham in the Europa League this season because considering their performance in the domestic League is not good enough this season. But it is possible that both can advance to the next round even though both are not good enough in their own League because I have seen in the last few seasons Sevilla have won the Europa League but in their own League Sevilla are not good enough in their ranking. That is why making comparisons like this sometimes will not be logical enough because the Premier League is a very competitive League for all teams so these English teams can make a difference when playing in other Leagues such as the Europa League.