I use a Canon 5D mark II which is similar to the 7D . You can select with the Multi-Controller button above the Quick Control Wheel.
However , I recommend that you use manual lens control for all focusing. The auto focus is not reliable, and to have out of focus high definition video is not a good look in Live View. It is better to use the the one red focus point and half depress the Shutter button ,( the is in stills mode.) then go to live mode to video.But, double check manually.