I just don't understand the continued hand wringing about our #2 GK. The #3 striker is a far more important and meaningful decision than the #2 GK (most likely). The #3 striker will have a chance for meaningful minutes at meaningful times - when we're chasing a goal, late in the game.
To that end, I think @alincoln has a good list, I would just organize it slightly differently.
#9 - Pepi, Sargent, Pefok
Wing - Pulisic, Weah
CAM - Reyna, Aaronson, Tillman
MF - M, M, A, LDLT, Acosta
FB - Dest, Scally, Robinson, Cannon, Yedlin
CB - Ream, CCV, Richards, Zimmerman
GK - Turner, Steffen, Horvath
That's 25, so room for 1 more. Need some another true winger or another #9 if we treat Sargent as a winger. I guess that means Ferreira and (gasp) Arriola are next up.
Edit: lots of flexibility here, obviously - CP10 can play centrally, Reyna/Aaronson can play wide, McKennie can play attacking mid, etc etc...
Edit 2: the more I look at this, we have a really solid damn team. It's amazing that we're all convinced that getting out of the group stage is a major win, largely because of the man in charge.