figured out the problem --

the zones table we're using has accents on french, spanish, and germanic letters. there are: "é" , "ö" , "ç", etc.

apparently those characters were conflicting with the canada post database, which was generating the error messages.

i updated the word "Québec" to read "Quebec", refreshed the checkout page (while logged in as a fake quebec customer), and everything worked fine.

i reproduced the error using several other zones with different accents (Galápagos, Oberöesterreich). each time, updating the zones table to get rid of the accent resolved the XML error.

so now i need to go through all 71 pages of the zones table and get rid of the accents...