-The Council received note of how I betrayed the Cerberus in the end
-The Quarrians and the Geth worked out a peace treaty to ensure forces against the Reapers
-The Krogans under Wrex's leadership took up a high time in weapon development and gatehred all clans to stand up agains the greatest trheat ever to come, granting the Krogans their well deserved battle of a lifetime with being completely wiped out or surviving as the condition of outcome, nothing better for a Krogan to fight hard than the though of instant deat hawaiting them
-The Salarians gathered enough information from Shepard's reports to evade the Council and launch a full out scale armada to aid him/her in the inevitable war
-The Turians rounded up all their mighty fleets to aid Shepard basing on the reports from Shadow Broker and testimony of Garrus.
-The Asari Join in the fight under the persuasion of the most noble warrior among the Asari - Samara
-The Alliance fleets Strike back at the Reapers quickly basing on the reports from Shadow Broker, and those of Shepard's proven being accurate.
-The Battarians join in to help saving their own lives, and maybe the rest of the Galaxy ...
-The other races help where they can.
-The Rahni Queen promised her aid when the time comes, lets hope she will remember that, you know, she is a queen, might be a bit busy

-The Geth are battle ready.
so the scenario is easy, Shepard, by logical terms, should by now in ME3 have the option to visit home worlds of Asari, Turians and Salarians, and possibly Earth (Come on! were Humans, 2 games without a visit home ?) firstly we should be able to visit Turians in the first place, persuade to your suicide plan (again, why is it suicide ? it's so easy to survive, it's actually hard to get killed!) stating where and when and how to attack Reapers when they arrive, showing weak points in their defenses and all that, which is easy cuz Reapers are high and mighty they will have little defenses,
then we visit Salarians and do the same, we should discuss the data we collected from the collectors ship, do remember that we do have obtained a formidable amount of data, before destroying the base, The Illusive Man doesn't know about it obviously, you can actually see the data shown to Shepard at the end of the game, Salarians can do a lot of good with that data, using the information against reapers is a good idea, but developing around that area is not smart, Reapers gave the tech on their own, just to wipe us out showing that we are of no match to them, even if we know their technology, Salarians will fix that attitude.
Visiting the Asari is gonna be quick at first, convince them to help, etc, do some impossible task, again, make em drop jaws. PROFIT.
now if my logic thinking is accurate, by now, the Geth and Quarrians either killed eachother out, or formed an alliance, and Tali is likely someplace in the center, maybe even with out child, dunno, if she is not gonna be a playable character (semi playable actually) then I do want to see her face, if I can have her on my team, I don't need to see her face, her presence is all I need

, back to topic, we should be able to easily convince both parties to cooperate and do some damage, after all, both races, the Geth and Quarrians are engineering experts, they should come up with some super damage sabotage when we need it

Also, I want Legion and Tali in my team !
The Alliance Fleet, they can fuck themselves, if they don't want to help, GTFO of my way, I bet the politics will do everything to NOT help, and will die a horrible death, and then Hacket (Admiral Hacket) will take on the leading role here.
then we just do some mundane missions, gather some resources, transform Normandy into a robot, and save the galaxy once again

well, not a robot but upgrading stuff, gathering weapons and armor, some tech, and wipe.