Just wanted to note, that for my Canon scanner, upon installing the drivers, only a scangearmp2 application is installed, which looks nothing like the ScanGearMP screenshots from the accepted answer:


Upon clicking Version, this is displayed:

The worst thing about this, is that I get no "raw" image - I only get JPEG (and JPEG is embedded into the PDF too), with all the loss in quality and blockyness that entails.
So:
other tools like Simple Scan or Xsane are not needed.
... well, if I had a driver connecting directly to Xsane, then I could get the raw image, and decide for myself how much loss of quality I want in my JPEG.
EDIT: It turns out for these versions of the drivers scangearmp2-3.40-1-deb.tar.gz, on Ubuntu 18.04, I in fact do have a SANE back-end:
$ sudo sane-find-scanner
# sane-find-scanner will now attempt to detect your scanner. If the
# result is different from what you expected, first make sure your
# scanner is powered up and properly connected to your computer.
# No SCSI scanners found. If you expected something different, make sure that
# you have loaded a kernel SCSI driver for your SCSI adapter.
found USB scanner (vendor=0x138a, product=0x003f) at libusb:001:007
found USB scanner (vendor=0x04a9 [Canon], product=0x180b [MG3000 series]) at libusb:001:010
# Your USB scanner was (probably) detected. It may or may not be supported by
# SANE. Try scanimage -L and read the backend's manpage.
# Not checking for parallel port scanners.
# Most Scanners connected to the parallel port or other proprietary ports
# can't be detected by this program.
$ scanimage -L
device `pixma:04A9180B_62FF57' is a CANON Canon PIXMA MG3000 Series multi-function peripheral
And then simple-scan connects fine to it, and I scan 1200 dpi into a PNG, so all is good for me :)