fiery printers and double sided printing

I typically do that with lpadmin. This is the command for a Fiery driving a Xerox XC570, but should be similar for a Fiery driving a Canon printer:

lpadmin -p <printername> -o EFDuplex=false

You can use the lpoptions command to find what options you can set:

lpoptions -l -d <printername>

Throw in a pipe to grep to look for duplex options and you might be in luck. Just test the settings to see what you get:

lpoptions -l -d <printername> | grep -i duplex

As always, TEST, TEST, TEST.

Here's how I did it: http://macmule.com/2013/07/16/canon-imagerunner-advance-c5240i-b2-printing-duplex/