How about the situation referenced here:  https://community.shopify.com/c/international-commerce/international-sub-domains/m-p/1191937

So would this work to have U.S. orders go to one 3PL and Canadian orders go to another?

I have exactly the same question.  Has anyone gotten an answer?  We'd like one Shopify site with separate 3PLs for Canada and the U.S...