My printer (Canon Pixma IP5200R) is capable of printing up to 9.600 x 2.400 dpi. However in 10.04 CUPS with Gutenberg installed lets me choose not more than 600 dpi in the settings. Is there a way using only open source to improve print quality? I already tried editing the *.ppd files to include higher dpi values. This indeed let me choose these values when printing but there was no visible effect on the resolution of prints.
The only way to improve quality of the print is to do the research of reverse engineering the specific driver related instructions and updating the pixma foomatic driver. Currently we don't have any Canon documentation to work from to get printers working.
I have a Canon iP5000 and have a limit of 600dpi too. Unfortunately it's a lot of work to reverse engineer hardware protocols and we're not likely to get much support from Canon or Canonical in patching the holes.