Canada can replace America as its biggest trading partner just as soon as it can develop new systems of distribution. Countries in Asia send us all their shit by boat across the Pacific; why don't you think Canada can figure out how to put stuff on boats and send it to China? It will disrupt their economy in the short-term, but that's a spit in the bucket. America, on the other hand, has to build its oil rigs, mines, and farms from scratch, which is a MUCH greater undertaking than the one Canada faces. Canada is much better positioned than the US.