Mass colossi until you get void rays. Then mass void rays until you get carriers. Then mass carriers while building more cannons. Make sure you upgrade and saturate your mineral lines. Use phoenix to lift up hybrids.
Massing Colossi on brutal? This didn't even work for me on hard. Being that they are so expensive, I had three problems when trying this:
1) I had very little resources to build air defenses or rebuild photon cannons after each wave, and since colossi can't attack air they were useless when zerg starts sending in flyers from multiple directions. 2) They are slow, and took too long to relocate at whichever choke point was being attacked currently if I decided to keep them together. If I kept them evenly distributed between all 3 chokes, there weren't ever enough of them to do enough damage before they got overwhelmed. 3) Even if I left them on the cliffs, they would be vulnerable to air attacks.
Maybe I'm just a bad player and I won't deny that possibility, but it just didn't seem like a very effective unit to me for this mission.
Well, I got over 1000 kills more then I needed on hard with this strat. Basically you're gonna fall back pretty fast, start making a decent amount of cannons. Then mass phoenixes *To lift the hybrids*. Void rays, for their great DPS. and carriers to distract. Just put em all in the middleish area. Pretty easy.