Hmm it seems amorin is really cooking, after making some nice signings of Mathew cuhan and mbeumo, he's now focused on a striker which sesko, Watkins and Jackson are all targets, and with the look of things I'm kind of certain sesko will be joining the red devils in no time soon and if this deal should go through mehn Manchester United will really be something else comes next season, just imagine the front line of cuhan sesko and mbeumo jeez they are really gonna Cook EPL defenders, like Truth be told Manchester United won't be an easy one comes next season if they should get sesko, and of course a better keeper then the rest is history.
Of the 3 names on your list, I have to eliminate Watkins and Jackson. Of course, they are familiar with the Premier League, but there is a reason why I say that. Watkins does have good statistics, but considering he is 29 years old, it indicates that he is not good enough for the long term for Man Utd. Jackson is still young, unfortunately I am not too impressed with his performance. Well, the most suitable is Sesko, young, has the DNA as a quality striker and I am sure Amorim can develop him. But getting Sesko is not easy considering that many other top clubs are also interested.