This is the current answer as of 9/15/2016.
Many thanks to Vuescan and Ed Hamrick!
Yes, you can use VueScan by downloading a compatible driver from Canon, but not necessarily the driver that Canon suggests.
After 2 days of fruitless searching, I emailed VueScan support: http://www.hamrick.com/support/
I sent them my basic info (scanner model, Mac system, etc., and got a simple and correct downloading answer on the same day, within a few hours. As a bonus, the VueScan interface is MUCH much better than Canon; We sent the $40 and got rid of the watermark as soon as we got the scanner up and running. They earned it!
I've used Canon products for many years, and always liked their camera and scanner quality, but this is unforgivable, nothing more than a cheap trick! If they wanted to charge for the correct driver, ok, but don't tell us to dump a perfectly useable scanner!