So itd be either
Depay - cavani - mata , with Rooney benched
Or
Depay - rooney - cavani, with mata benched
Rooney is undroppable. LVG has already made this totally clear and demonstrated this in every game last year.
Cavani - he isn't a Utd player, so I don't understand why you are including him in our line-up.
Depay - you expect an unproven player (in the EPL) to start ahead of Young? Young, who was one our best outfield players last season?
IMO, our first choice front 3 will be:
Young - Rooney - Mata
Depay will provide cover for Young and Rooney.
Valencia is available if we need a RW.
Fellaini is also available to play in the front 3.
Wilson can provide cover for Rooney.
Another striker (probably Pedro), may also be an option if to provide cover for any of the front 3.