With discontinued products, it's up to the manufacturer to write drivers, and it looks like in this case, Canon decided it wasn't financially economical to rewrite the drivers.
You might want to try XP Mode, which is a way of running a 32 bit XP operating system within Windows 7: http://www.microsoft.com/windows/virtual-pc/download.aspx
The other option is to get something a bit newer, that does have 64 bit drivers. http://usa.canon.com/cusa/consumer/products/scanners/photo_scanners