Thanks nos1609, maflynn and SG. I reported the issue to Apple, using the Feedback Assistant and to Canon Support. Canon Support replied: ' Please be advised that there is no driver or software for the CanoScan 9000F released from Canon that support OS X 10.11 yet; this could be the reason why you are having this issue.' So it looks as if I will just have to be patient.
Canon IJ Network Scan Utility for (Windows Vista 32bit/64bit, Windows XP SP2/SP3/Windows XP x64 & Windows 2000) File Name: ndwin250a_ntwin250aen.exe Download. IJ Scan Utility (OS X 10.12/10.11/10.10/10.9/10.8) Description: This is an application that allows you to easily scan photos. Serves to enable the relationship between Canon 8800F scanner with a computer or Mac device. The drivers we provide support the install for compatible operating systems like Mac (OS X) and Windows. However, we recommend you to setup driver CanoScan 8800F scan according to the version of the current operating system.
They did suggest that I try using a different USB cable, but that didn't make any difference. I wasn't able to use the Image Capture app.
I have Canon mg5450 and it is so much trouble to use with Apple that I have simply given up on it despite recently spending a fortune on ink. Canon products simply do not play nicely with OSX. Very good print quality, but driver support with OSX is utterly useless and I have spent more time trying to get the damn thing working than I ever did printing and Canon technical support is useless. I have decided to take the advice of Apple technicians and buy a HP printer.
Not as good print quality, but a printer that works consistently is better than no printer at all.