show the scanner? lsusb -v will give extra information.
Presumably it will show the printer part at least, but maybe the scanner
is there as well?
If it is there, then you can find the
vendor ID, product ID and serial number
and use that to form the device name as described in the man page.
(sudo less /var/log/messages might also show you this information
but you will need to search for it).
It looks as if you may need to add that to /etc/sane.d/pixma.conf