For that model printer, on the LCD screen of the printer if you go to menu -> settings -> device settings -> lan settings -> wlan settings
That is where you need to go to establish the wireless network connection from the printer to the router. If there is an easy setup wizard there, then choose that option. I think the only choices are using WPS or WCN. If your router has a WPS button on it, then you can select the WPS setup there and then push the button on your router to establish the connection. If your router does not support WPS, then try this alternate method to get the wireless setup.
The other method to setup wireless is to temporarily connect the printer to a laptop with a USB cable, then use the Canon LJ Network tool to configure the wireless settings. You may have the LJ network tool already on your laptop under start -> all programs -> canon LJ network utility. If you do not, you can download and install it from the canon website here.
Scroll down and select your operating system, then the tools is under the software section.
If your printer is connected with usb, when you open the tool it should see the printer and allow you to enter the wireless details by going to configuration -> wireless lan
An alternate method of establishing the network link, if your printer is located in close proximity to the router you can simply run an ethernet cable to connect the printer to the router. This is easier and more reliable, and the laptops can still print wirelessly through the network.
Let me know if you have any questions, or run into any problems trying to get the wireless connection re-established.
If you have not modified any settings yet and it worked before, you may simply try turning off the printer, unplugging the router and then plugging back in. Wait a minute and then turn the printer back on.