Earlier this month, it was revealed that a possible fighting game based on the JoJo?s Bizarre Adventure series is being developed by Soft Circle French Bread. Now, it seems that the source who originally leaked that the game is in development has also revealed the possible roster for the upcoming game.
The leak, which comes from Dasvergeben (via Shoryuken)- a renowned leaker in the fighting game community – states that the game will have a 36 character base rosters, including:

Jotaro Kujo
Young and Old Joseph Joestar
Johnny Joestar
Jolyne Cujoh
Yoshikage Kira
DIO
Jonathan Joestar
both Josuke Higashikatas from Part 4 and Part 8
Koichi Hirose
Gyro Zeppeli
Jobin Higashikata
Noriaki Kakyoin
Muhammad Avdol
Jean-Pierre Polnareff
Iggy
Giorno Giovanna
Robert E. O. Speedwagon Caesar Anthonio Zeppeli
Kars
Wamuu
Hol Horse
Okuyasu Nijimura
Rohan Kishibe
Trish Una
Guido Mista
Diavolo
Narciso Anasui
Ermes Costello
Funny Valentine
Diego Brando
Dio Brando
Father Enrico Pucci

According to the leaker, the last two characters are currently unaccounted for, but the game will apparently feature a wide range of DLC characters as well. Per Dasvergeben, the game will have two Character Passes that have 6 characters in each, which would bring the total game roster up to 48.
According to him, the DLC characters they?ve heard about include:

Vanilla Ice
Pet Shop
Lisa Lisa
Esidisi
Rudol Von Stroheim
Weather Report
Emporio Alnino
Straizo
Akira Otoishi
Yukako Yamagishi
Pannacotta Fugo
Bruno ...