It feels really awkward. Manchester United are 16th and Tottenham are 17th in the PL. But they are playing against each other in the EL finale. One of the weirdest scenarios ever. 
But anyways... IMHO, Amorim's club is closer to the trophy. Why? Because Manchester United have a much better history in European competitions. This is my reasoning. I'm open for being surprised by Tottenham also but this is my thinking.
I don't know how Manchester United and Tottenham Hotspur managed to beat the clubs they faced in the UEFA Europa League competition to become the UEFA Europa League finalists when they are struggling and they haven't won a match in the Premier League table for a very long time. With the situation surrounding Manchester United and Tottenham Hotspur in the Premier League, both clubs will take the UEFA Europa League final very seriously in order to secure a spot in the UEFA Champions League next season, which will make both clubs put in their best to win the final. The final won't be easy for Manchester United, but I believe Manchester United will edge Tottenham Hotspur in the final, just like you said.But anyways... IMHO, Amorim's club is closer to the trophy. Why? Because Manchester United have a much better history in European competitions. This is my reasoning. I'm open for being surprised by Tottenham also but this is my thinking.