I had the same problem with the origin postal code.
Thanks to RCAF for the initial reply, I tried that and it worked.
An additional thanks to binare, for the corrected code that gives the original functionality. That worked for me too. Just as a note, the full code that needs to be replaced is on line 67
Replace:
$this->_canadapostOrigin(STORE_ORIGIN_ZIP, $country_name['countries_iso_code_2']);
With:
$this->_canadapostOrigin(SHIPPING_ORIGIN_ZIP, $country_name['countries_iso_code_2']);
This worked perfectly for me.
Thanks again.