OK, I took a look at linuxprinting.org and found out that they recommend the gimp-print driver for Canon S450 printers. Now, CUPS is a very complicated system and it usually needs also Ghostscript and sometimes also Foomatic filters to work.
By chance I've noticed that, due to complex dependency resolving mechanisms in Debian's APT (Advanced Package Tool) system, you can install all the needed packages for CUPS, Ghostscript and Foomatic with a single command: "aptitude -r install foomatic-bin". Please, try it to ensure that you've got all the packages that CUPS needs to work.
After doing this, the only additional package you'll need is the gimp-print driver that linuxprinting.org suggests for your printer. In Debian the gimp-print driver for CUPS is included in a special package, cupsys-driver-gimpprint, which you also need to install (apt-get install cupsys-driver-gimpprint).
After executing these two commands, you should probably reboot your computer and then point the webbrowser to the http address localhost:631/admin to configure your Canon S450 printer. I hope you can get your printer working all right following these tips.