I've been slaughtered by this strat to as Protoss.. I even put up 2-3 canons at each expo while massive stalker and a few observer but then the banshees just took out the canons 3shots each :I and then my obs were sniped = GG
Only way to defend against maybe 8-12 banshees 2-4 vikings, 1 raven would probably be to stick 2canons with 4-6 stalkers at each base and slowly but safely macro up until you can counter attack forcing your opponant to use his flying ball of units. honestly don't see any other way.. so useless leaving stalkers not doing anything, gl! :)