There is a menu option (Communication I think) on the Canon 20D that needs to be set to 'PTP', not 'Normal'
Edit : and there is also this article about the 20D http://support.apple.com/kb/TA24008?viewlocale=en_US
Message was edited by: King_Penguin
Another solution would be to find a Compact Flash-to-USB card adapter that is compatible with the USB adapter in the Camera Connection Kit. Some such adapters draw too much current from the iPad.
You can also get a Secure Digital-to-Compact Flash adapter that would allow you to use SD cards in your camera.