You don't feed ANY volts into the connector.
According the your link the external remote works on the G12 and EOS DSLRs so you google 'Canon remote shutter pinout' and find something like http://www.doc-diy.net/photo/remote_pinout/
which tells you that the camera expects 2 switches at the end of the cable.
You could probably do it with transistors instead of mechanical switches if you use a multimeter to determine the voltage on the 'focus' and 'shutter' wires.
Do not connect these wires directly into an arduino or any other microcontroller.