Flowing Fix: Clear your printer queue on Mac OS X

via: http://forums.techguy.org/apple-mac/1062988-solved-canon-ip6700d-printer-wont.html#

If you are having trouble deleted a file from your printer queue, you might have to resort to a terminal line command.

1) Open up "terminal" by searching for it with Spotlight or going to "/Applications/Utilities/Terminal"
2) then, at the prompt type the following:
    lprm -
3) This should remove it from the queue.  If not, you can reset the print system.

If step 2 above did not work: To reset the print system, go to the printer system preference dialog, right click your printer and choose reset print system. After which you will have to re-add your printer.