I found a YouTube video on how to rid OS Mavericks of Canon printer/scanner software, and revert to OS Lion drivers and utilities. Unfortunately it didn't work with my MP450, and MP Navigator is now non-functional. This is turn led me to looking for a new Canon Multifunction machine, and I take note of the suggestions in this thread.
Two things:
1. I have learned the hard way that OS updates are not always a good thing
2. I wonder why Mac users don't partition their HDs to accommodate two - or more - OS (I know it depends on the ROM version as to whether or not this can be done). Dual partition and OS is how I've worked round the printer/scanner (I use the 450 for scanning only) issue, ie. I reboot into Snow Leopard from Mavericks, and I can scan to my heart's content. An inconvenience? Maybe, but cheaper! ;D