I fly the 319 and to be honest, my technique isn't much different whether using Flap 3 or full. The only difference I find is the slightly higher nose attitude and the fact the aeroplane feels a little more "slippery", so to speak.
In terms of flare, I still close the thrust levers around the same point, i.e. around the "30" auto call-out (plus or minus a bit depending on head/tailwind conditions of the day); for Flap 3 I find I flare ever so slightly later and obviously a little bit less due to the attitude already being higher. Other than that, I find there's little difference between the two.
I can't really speak for the A320 or 321 but with the higher weight I suspect there might be a bit of a difference? I note the poster above who mentions the huge difference in attitude between F3 and F full on the A320.