Canon provide Debian Packages to install the driver under ubuntu for download. Offical supported is only the previous version 10.04 of ubuntu. Extracting the zip file you will find under
the deb packages. First thing to install is cndrvcups-common_2.20-l_i386.deb with dpkg -i <deb file>. The problem is that ubuntu 11.04 doesn’t contain the required gs-esp package.
Workaround is to download and install it with
dpgk -i gs-esp_9.01~dfsg~svn12047-0ubuntu1_all.deb
After that you can install the common canon driver and afterwards the ufr driver:
dpgk -i cndrvcups-common_2.20-1_i386.deb dpgk -i cndrvcups-ufr2-uk_2.20-1_i386.deb
Now you can open the driver setup application and click on the add button. Choose network printer, enter the ip of your canon printer and click on examine. Select from the list below Canon and click on next. Select “LBP6650” and click on next. Confirm dialog with use button. Test your configuration with printing a test page.