Essentialy, the cannon trick is that when both towers are cleared, you send 2 ranged dps and most likely the tank on the right tower, get the tank in the cannon and chain stun Galakras while it's in the air. The 2 dps burn down Galakras while it's in the air while being stunned while the rest of the raid stays down, dealing with adds as they come. They'll come infinitely, and since there's no enrage timer before you get Galakras down, you can do this for a long time.
Once it's life is around 20% or 30%, you bring it down. It's life doesn't reset when it comes down, so it comes to burn phase where the boss has like 20% health, making it stupidly simple.
The only real issue is that the adds never stop coming while you're burning the boss down, but it's really not that hard to deal with if you have good healers who, at this point, basically have unlimited mana. So if you can kill the adds with 3 DPS + a tank then you're golden! You can even send your weaker ranged DPS up there because it's essentially a rotation burn on the boss, which is always easy, and you can take all the time in the world.
Nobody knows if it's going to get fixed or not, but hey, if you can do it now... It's not like it's a big exploit.