Here is current status for canon driver hack: 
The canon package is here: https://packages.gentoo.org/packages/net-print/cndrvcups-lb
The ebuild comes with it has lots of dependencies, complies gui parts and deploy binaries.
To compile and test the driver, the following hacks must be done:
1. Go to Sources/cndrvcups-common-3.80/buftool, compile and install libbuftool. This is a static library, thus only used during compile.
2. Go to Sources/cndrvcups-lb-3.40/pstoufr2cpca/ and compile the filter. Deploy filter and ppd files to chrome book.
3. The filter will call ghostscript with device=opvp, opvp support is not currently compile in our gs. To hack this for now, comment out "--disable-contrib \" in https://chromium.git.corp.google.com/chromiumos/overlays/chromiumos-overlay/+/9597a8311859ca8eac99459e6bf860cc72055ada/app-text/ghostscript-gpl/ghostscript-gpl-9.19.ebuild#
4. Ghost script need device driver, the device driver is cndrvcups-common-3.80/c3plmod_ipc. Deploy the shared library to chromebook. (How to use this in the components is still an open question.)
5. The driver will call into some closed source code, per https://wiki.linuxfoundation.org/images/6/65/MontrealSummit-2007-Canon_Printer_Drivers_for_Linux_070926-2.pdf.

Will talk canon to see if we can get support here.