Assuming 12 pitchers come up north, projecting the 25:
C: Vasquez
1B: Napoli
2B: Pedroia
3B: Sandoval
SS: Bogaerts
LF: Ramirez
CF: SOMEBODY
RF: Victorino
DH: Ortiz
4 roster spots left
Backup C: Hanigan
Backup IF: Holt
Backup OF: Craig, Nava
Centerfield is the only position where we have minor league options left - so 2 of Betts, Castillo and Bradley will be in AAA (I include Bradley because I am a nice person). Now, theoretically the team could cut Nava (they could cut anybody, but assuming a realistic maximum the team wants to eat). But otherwise something has to give numberswise.
Now if the Red Sox bring 11 pitchers - which is possible but I doubt myself - Castillo might be the next man up. But if that's the case, Bradley might be a better choice early. This would give Castillo regular game reps (for a guy who has not played much baseball lately), and an excellent defensive CF replacement since I am deathly afraid of Victorino breaking in half.