Your United bias aside, you have to remember the facts:
City have an option, Dortmund has to inform them about every offer and they have the right to increase that sum. This option alone will result in a bidding war (If i think about it it was very very clever from Zorc, in the negotiations with them to buy Sancho it sounds like its a pro-point for City, but it the end its also great for BVB).
Sancho is one of the best youth prospects out there, in a market which became crazy, and still got contract till 2022 (thanks Sancho for extending it last year
), so BVB can lean back and wait until some offer fits their imagination. The background of all this is that Sancho feels great at Dortmund, knows what he has got there, and there is an (oraly) agreement which says we let you go if it make sense, but only if the offer fits our expectations.
My bet is on 2 teams:
Liverpool
Real
In this sequence. With Liverpool are connections through Klopp, they play thrilling football and are the hottest thing in the PL, and could afford him. Real always want the shiny things, and we got Hakimi from them so there might be some negotiations, Watzke got a connection to Perez and negotiations were always fair.