There is a good description of the silk trains in Canada at the link. CPR dominated with their own steamships. The trade in Canada started in 1887 and petered out in 1930s with the depression and competition from Japanese ships using the Panama Canal to get to New York. Eventually rayon replaces silk. Special lighter weight cars, shorter than box cars, equipped with passenger car trucks were used to transport raw silk on special high speed trains that had the highest priority on the railway. The market for the Canadian railways was also in New York.

The silk cars later showed up in express baggage service. They had distinctive centre doors and were shorter.

Malcolm Vant

https://www.canadashistory.ca/explore/transportation/canada-s-silk-road