On the 5d and 5dII, you enable MLU with AEB and the 2 sec timer. Press the shutter release and the sequence of three shots is taken after the timer countdown. In between each shot, the MLU will be active, so the mirror will flip up, the camera will "wait" and then the shutter will open.
If you use MLU manually (with no timer) then you press the shutter release once to flip up the mirror and then press again to release the shutter (so you control the "pause"). This sort of defeats he benefit of MLU because you have to touch the camera again to release the shutter.
I have not used a 7d, so I apologize if this does not apply to the 7d. Also, you may get a similR benefit from shooting within Live View, as the mirror is locked up in LV mode.
Kirk