If Canon haven't released a Windows 8 driver for that model, they are unlikely to do so in the future, and you won't find one anywhere else. Just be content that you can still use it. There is an alternative method:
Uninstall the Windows 7 driver.
Download & install "VueScan" trial version: http://hamrick.com
If it works with your scanner, buy the program for $40 US Dollars.