The IP address is assigned automatically by your router using a protocol called DHCP (Dynamic Host Configuration Protocol.) The word 'Dynamic' means it can change at any time, so your printer's IP might be different every time you check it.
Many people don't know that networked devices can also have a 'static' - i.e., fixed - IP address. That's particularly useful for a printer, because it makes it easy for you and your software to find the printer on the network.
- You'll need to know your printer's MAC address, which looks like this: 12:ab:12:ab:12:ab:12:ab
- Open your router's administration console and find the network map
- In the network map find your printer's MAC address and right next to it you'll see the IP address assigned by the router.
There may be other ways to find the IP address, but the above method always works.
Another advantage to giving your printer a static IP address is that you can type that address into your web browser to see the printer's own administration console.
EDIT:
Canon includes a utility called the Canon IJ Network Tool. Open that, and from the Settings menu select Configuration. You'll see the printer's (current) IP address.