The Red Sox can bring 30 players to Japan, 28 of which will be eligible to play in the games against Oakland, with the normal 25 man roster in effect for those games. In other words, two players will go to Japan but CANNOT play in the games against Oakland, and three players will be healthy scratches from the day of game roster.
So here is the 30 man roster for the trip:
Wakefield and Buchholz are slated to start the two exhibition games, which means they're the most likely candidates to be kept off the 28 man roster. Then I'd bet that Lowrie, Brown, and Moss are the ones kept off the 25 man roster.