I have the same Rebel T3, but have no idea what the ideal settings for it are. I just started playing with HDR this week. I just play until I find a setting that I like, and go with it for a few. But then again I'm just now learning how to manipulate a camera.
The one thing that I would add to mistermonday is to turn the autofocus off when you are ready to take the shot(s). Set your focus prior to taking the picture with the autofocus on, but switch it to manual before shooting it. I haven't seen it happen yet, but I imagine that the focus could shift in autofocus on between the three shots.