this worked for me
Last week I suddenly began getting the same "printer is offline" error when all had previously been working fine. I tried downloading the latest driver, deleting and re-adding the printer, rebooting the network, reinstalling the Canon software, etc. to no avail. It was becoming puzzling and quite frustrating.
Glad I found this thread - using the Reset Printing System option in System Prefs resolved the issue. It also worked for my wife's laptop, which had previously been accessing our printer through my desktop via Bonjour. She is now able to print through our wireless network without having to turn my computer on.
Many thanks to jswallac and seamd73!
Specs, for the record: Mac Pro 2 x 2.66 GHz, OS 10.5.8 & MacBook Pro 2.4 GHz, OS 10.6.8, Airport Extreme 802.11n (4th Gen) router, Canon Pixma MP495 printer