First, you should update to 10.6.8, most easily accomplished by running software update. There are some printer drivers included in some of those updates.
Next, you didn't indicate what model your Canon printer is. That would help in troubleshooting.
Third -- have you power cycled your printer? Also, some of those dialogues showing "printer offline" provide a button to "take online." Is there a button or option for that in your dialogue?
Fourth -- I have a Canon printer (MG8120 model) and after upgrading one of our iMacs to 10.6.8 I had to reinstall the original Canon printer software and drivers from the CD's that came with it. Then it worked fine.