Well, in ME2 you had multiple squad members who could do Biotics: Samara, Miranda, Jacob, Thane, and Jack, and each served a specific role: Samara was long range firepower and biotics, Miranda was biotics and tech, Jacob was biotics and long range combat, Thane was the same as Miranda (IIRC), and Jack was pure biotics.
Essentially, what they did was take the three Biotic squad members from ME1 and divide them up. Thus Wrex's Biotics and Combat became Samara and Jacob, Kaidan became Miranda and Thane, and Liara was Jack. Now, since we know that they're reducing the squad size, to my aforementioned 8-10, gives us a rough idea of what the remaining squad members will be. Liara has pure biotics covered, and she's a non-contingent squad member (ie you get her no matter what), so we can rule out Jack. Kaidan is Biotics and Tech, but as he's a contingent squad member, we'll likely see a Kaidan substitute (most likely Miranda) if you'r playthrough doesn't include him. That leaves us with Biotics and Combat, which most likely will be filled by a new character, as I can't see anyone who'd really fill that role. Wrex would make sense, but then it's pretty much the ME1 reunion tour, and god forbid we have that. Samara might work, but she doesn't really fit, and she's doubly contingent (she can die, and even if she survives is sworn to kill Renegade Shepard.) Maybe Thane or Jacob, but I doubt it. My guess is there are new characters for each combat role. We know that Sanders is a soldier, so that leaves us with Sanders-analogues for Biotics and Tech.
The squad is most likely going to be composed of, and remember this is a total guess, five returning squad members (Liara, Garrus, Ash/Kaidan, Tali, and one more (Most likely Miranda)) and three new characters, each fulfilling one of the class roles. Also, pretty much everything I just said applies to the other class roles.