The technical specifications for Canon mf635cx printer mention support for "UFRII, PCL 5c*, PCL6, Adobe® PostScript".
But I see that the
Open Printing organisation does not have a driver for it.
For FreeBSD, my suggestion would be to install and use
print/cups package and use one of the generic PCL6, or PostScript drivers.
I suspect that the
print/gutenprint package may help with driver options, as may
print/hplip (if you choose PCL5c), as indicated by the
Open Printing Generic PCL 6/PCL XL Printer document.
However, you may be able to get a suitable PPD file for UFRII from Canon's Linux package
linux-UFRII-drv-v510-uken-19.tar.gz. Look in the "Sources" directory.
I'm suggesting CUPS over lpr/lpd because it generally works quite well and so many of the FreeBSD packages drag it in as a dependency.
However if you wish to use lpr/lpd the
FreeBSD handbook and even the
Linux foundation may help with generic PCL6 and Postscript configurations.