One explanation for this difference is that Canada has always been dependent on trade. We were founded on a resource-export model, and since trade started out being very important, there is less room for its importance to grow.
But, in my opinion, the basic insight here is that US companies pursued globalization and offshoring more than Canadian companies did, boosting the importance of trade to the US economy more than was done in Canada. When a company procures one slice of its value chain offshore, it does so to reduce costs.