The game has 15 characters divided into 5 teams. Let's guess the roster.

Sonic Tails Knuckles
Shadow Rouge Omega
Vector Espio Charmy

This is where it gets tricky. Amy will be playable but her partners are up in the air. I do not expect Big or Cream because they havent been relevant in awhile. They didnt even show up as cameos in Forces. Doctor Eggman, Silver, and Metal Sonic are also expected. Hell, maybe even Infinite

Doctor Eggman Metal Sonic Infinite?
Amy, Silver, Blaze?

I forgot about Create a character ...hmmmm

Amy Silver Create a Character?