Here we go again! Thanks a lot!
I was aware that there is the SANE-solution, but at the time of my Mavericks post, it was not yet compiled for 10.9...
Some comments from my install:
I have a LiDE35, which gives me a USB ID of: "usb 0x04a9 0x2213" in the Sane Prefs Panel.
Still, I could not see the scanner, but the only point where I slightly stepped out from Dtermined'sinstructions was that I was not sure, which version if the Canoscan Toolbox I was using exactly. So I digged deeper and found that due to my location in Germany, I was always directed to the German website of Canon, and I used the search-function, which always gave me the most recent version of the Toolbox, which is something with a 5 in front, say 5.0.14. This one could not open the driver.
I then wanted to make sure that I get the "Canoscan Toolbox X software from canon us site use the version for OS 10.6" as written in the post and forced the canon _us_ site, did not search but click through all products, select the old version, which eventually gave me the file: cstbosx4512ej4.dmg For all of you who do not want to click like mad, this is the filename to google for...
This one installed works like a charm, without scanner buttons, but who cares.
Thanks to everybody contributing; talk to you again after the next OS update :-)
Cheers.