Spoilers ahead.
I think the game will make you chose between Wrex and Grunt at some point because I think Grunt will try to take over Clan Urdnot, in which case I'll choose both on different saves
Garrus will be there, but depending on how you molded him(aka letting him kill doctor saleon or not in ME1 and letting him kill Sidonis or not in ME2) he will be either a real stand up
guy, or ruthless like Saren.
Tali will either be a fleet admiral for the Quarians or come back to lead some kind of revolt(if exiled). That said, she won't be a squadmate. You might say: "What about the romance?" I say: No idea, but if you didn't romance her and Reegar lived, guess who gets her.
Legion will be there(if you didn't send him to Cerberous,) but even if he's not, you will probably be able to control the Geth(Via Overloard and Quarian help).
Mordin will be there, he will either cure the genophage or not, depending on how you influenced him.
Miranda, well if you saved the collector base sure, if not and she sided with you, that will cause problems because Cerberous is hiding her sister.
Samara said something about "call upon me and I shall come"(on my paragon save) and when you first recruit her she said"I may have to kill you after our task is complete if I find you go against the code, so if your a renegade, she'll probably try to kill you.
Jack-Homicidal Killer if you encouraged her to shoot that guy in her old cell, if she spared him, perhaps not but with Jack, who really knows?
Ashley/Kaiden(baby boy as I call him) Might not join you if your still Cerberous, I don't fully know how this will go down.
Liara- I have no clue, if she becomes a squadmate after Lair of the Shadow Broker, that could be problematic. Either way if she comes into the next game, she will be the one to join you no matter what path you take(granted this is before Lair of the Shadow Broker so her attitude will most likely depend on that mission)
Thane: Well he will be in the game, perhaps on his deathbed, or maybe theres a cure and you can find it, maybe Mordin cures him, not sure, but seeing how popular he is, I'm 100% sure he'll be there in some capacity.
Kasumi: Well whatever was on the Graybox will come back to haunt her, and it will be interesting to find out what beg secret was on there.
Zaeed- This I don't know, maybe he leads the Blue Suns if you killed Viggo, but if not and did the paragon way, I have no clue, he may not even be a squad member, if not, good riddance old man.
Jacob: Don't care at all, no theories on this guy. Maybe he'll get a dog.
SPEAKING OF DOGS, wouldn't it be cool if there was a German SHEPARD on the Normandy?
New Squadmates: There will be some for sure, especially if you killed off almost everyone in the final mission.
As you can tell, I love talking Mass Effect.