I’m the OP. I can tell you that attempting to print a PDF from Okular or even a TXT from Kate with “Letter” page size onto Letter paper in the printer results in my printer (Canon MF4370) printing one distorted page with print spilling off the edge then throwing an error (on the printer LCD) asking for A4 paper to be loaded.
Printing an ODT from Libre Office or a webpage from Firefox works OK.