Marines counter Zealots if you have Medivacs + Stim Pack.
Marauders should be focusing on Stalkers first but they can also fire at Zealots.
Ghosts counter High Templars with EMPs.
Medivacs should be slightly in the back curing marines.
Vikings counter Colossi (also Siege Tanks).
Sentries are best countered by Hellions, Banshees or Siege Tanks, but they are a relatively weak unit so you can kill them anytime but better as soon as possible (especially for those force fields that split your army = death).
I'd keep marauders in the front and marines slightly in the back with medivacs curing them. Bring Vikings to the front, snipe the colossus and bring them back immediately. Stalkers will snipe down your Vikings if you don't make sure they're only there sniping and brought back. Also don't position Vikings directly above Stalkers. They will die like flies. You can transform them to ground units for additional firepower later (it never harms).
While they're busy sniping the colossi, get the ghosts (possibly cloaked) and emp the Protoss army but aiming at the high templars. High templars without shields = dead. If the High Templars are clumped together, EMP is better than sniping, since you hit all of them at once, but if you see one at a time, then sniping might be a better choice. EMPing doesn't just lower shields but also reduces energy for spellcaster units. So you should keep this in mind when deciding between Snipe vs EMP.
This is what I would do. It's task-intensive so it might help to use unit groups.