1Ds3 - 1 point focus
See page 88 of the User Manual:
Press the focus selection Button # (top right of the rear thumb-sholder buttons, also used to magnify the play back image). The current AF point will light in the viewfinder.
Select the AF point you want active. Turn the main front control wheel left or right until all the peripheral AF points light up, automatic AF point selection will now be in effect. Or by pressing the centre of the joystick in, you can select/toddle the center AF point or automatic selection.