I will try to use as few cannons as possible because it can't be used offensively by AI's.
I think dragoons are good against terran
Without a good micro it's not so powerful against marines and tanks will probably destroy them, maybe a mix with some zealots or dark templars.
By the way, I'm testing transport right now, here is a blank replay in free for all for the 3 races, on an Island map.
I have been able to do some mass droping using 5 shuttle simultaneously, they were quite well coordinated.
It's also possible to choose what units you want to attack with, and shuttles will carry them. So maybe a shuttle-reaver attack is possible (without micro though).
I have tried on ground maps but the AI didn't use the shuttles, anyone knows if it's possible to make it using them ?
I tried adding them to attacking party but they just went to the attack point and came back to my base.
I think I have found what caused me problems in cheating scripts, when the AI gets a critical mass of units (for example 12 zealots) and the opponent doesn't have some units (or buildings, I don't know), all its units wil automatically attack the weak opponent. This may be some hardcoded thing, did you experience the same problems ?