The easiest and the first thing which every person going through "Canon Printer Offline" issues needs to do is resetting their printer by turning it on and off.
You need to hold the power button for a sometimes and allow the device to shut down completely. You can simply remove the power cable from the device. Now to turn the printer on, you need to press the power button for a sometime again or you can plug the power cable back again. After this wait patiently for a while so that the device could reboot completely.