Your two enemies will mostly be fighting amongst themselves, but will send small assault teams to hamper your progress. The Zerg will constantly push back the Tal'darim, making it the main focus of the map. This mission is a three way battle against the Zerg and Tal'darim.
When ready, destroy base two in the same manner and upload to the last two broadcast towers. With this building gone, you'll gain access to a secret mission. It can't be targeted with a normal attack, so you'll need to use an area effect attack. While here, send a thor to the south-east corner and destroy the science building. The Dominion will send in back up as you upload to the broadcast tower, but a good number of thors and vikings will subdue them. Once you have a good number of thors, assault the third base and wipe out the defenses.