In addition to what Bruce said, you need to know the time frame and what Canada was permitting to be imported from the US. Were the crops quarantined? Canada did quarantine many US crops. If they were quarantined, then the crops would be offloaded at the point of entry and held for the required period. The loaded into CN and CP reefers.
I believe that CN was independent and not part of the US pools.
You MIGHT find any of the reefers listed. The question might be better phrased which would be most likely?
That leads to the need for greater specificity. What cargos were being shipped? What is the season being discussed? I could rationalize pretty much any of the reefers listed based on specific cargos being shipped from the US.
A question from Drew Bunn...
Just wondering if anyone could tell me which of the western roads' reefers I might find on a Canadian National train in the 1950s. Santa Fe? WP? GN? Was CN part of the PFE/WFE/FGE pools? All I seem to find is information on the CN reefer fleet.
My interest is in Ontario and the Atlantic provinces.