Just an update for anyone who's interested. The current roster for the new PSP game is as follows -
All the characters from Battle Heroes (i.e. everyone playable up to and including SB2 Heroes) plus the generals of Sekigahara. Whether or not they'll add anyone else from the third game or Hisahide as NPCs is unknown.
For those still not sure, here's the list of names:
Date Masamune
Sanada Yukimura
Tokugawa Ieyasu (both versions)
Ishida Mitsunari
Maeda Keiji
Chousokabe Motochika
Mouri Motonari
Katakura Kojuro
Azai Nagamasa
Oichi
Fuuma Kotaro
Takeda Shingen
Sarutobi Sasuke
Uesugi Kenshin
Kasuga
Oda Nobunaga
Akechi Mitsuhide
Toyotomi Hideyoshi
Takenaka Hanbe
Nouhime
Mori Ranmaru
Maeda Toshiie
Matsu
Itsuki
Xavi
Shimazu Yoshihiro
Honda Tadakatsu
Imagawa Yoshimoto
Hojo Ujimasa
Honganji Kennyo
Miyamoto Musashi
That's 32 characters overall counting the two of Ieyasu. The official website hasn't been updated yet, so we'll see what happens. Thanks to koeiwarriors for translations.