My assumption is as follows:

UNITS (Covenant ... Humans)

Drone ... Infantry
Grunt ... Marine
Jackal ... Sniper unit
Elite ... Spartan
Hunter ... <>
Engineer ... Medic

VEHICLES (Covenant ... Humans)

Drop Ship ... Albatros Drop Ship
Banshee ... Skyhawk
Phantom ... Pelican
Shadow troop transport ... <>
Wraith ... Scorpion
Spectre ... Warthog: Gauss
Ghost ... Warthog: Standard
Shade stationary turret … <>
Shielded plasma turret ... M247 mounted turret
portable plasma cannon ... M247 portable turret


If you don't know what any unit/item is, check out Stephen Loftus's scale comparison @ HBO.

NOTES:

1. Since there are so many units & vehicles, it's logical to assume some units (ODSTs, Brutes, Seraphs, Interceptors) and a third faction (the Flood) will be saved for the next game.