Hi Topcat138,
To try and resolve the envelope printing issue, we recommend reinstalling the printers using the latest drivers from the Canon USA website. The drivers for the PIXMA MX920 series printer can be downloaded here, and for the PIXMA MX320 here. You will want to download and install the MP DRIVERS file from the DRIVERS section of the webpage for each printer.
Should you still experience difficulty after reinstalling the drivers, we ask that you please contact a Canon technical support representative here for further assistance. A representative will be happy to assist you free of charge.