Recently ran into a printer from Canon, model LBP6300dn which doesn't seem to be supported by either net-print/gutenprint or net-print/cndrvcups-lb
Found some drivers from following Canon page in a package called as
"CAPT Printer Driver for Linux Version 2.60"
Installed extra packages:
After more digging, it seems that some of the Canon printers use protocol called CAPT printer stream - https://help.ubuntu.com/community/CanonCaptDrv190
And also following ebuild: http://gpo.zugaina.org/net-print/cndrvcups-capt
*** This bug has been marked as a duplicate of bug 130612 ***