Go to their website. The driver model for Windows last changed with Vista, so Windows 7 and 8 should both use Vista drivers. Vista was Windows 6.0, Windows 7 is Windows 6.1, and Windows 8 is Windows 6.2, they all use the same drivers. Just make sure you get the right bit'd drivers, either 32-bit or 64-bit.
Go here, select Drivers & Software, then pick Windows as the OS, then select either Windows 8 or Windows 8(x64), then click on Drivers, then download the Windows 8 drivers.http://www.usa.canon.com/cusa/support/consumer/scanners/canoscan_series/canoscan_lide100