I'd argue the US has, at the very least, a moral obligation to not make a deal with China which precludes releasing those Canadians.

Furthermore, I'd argue that it's in the United States best interest to do so (since it will affect the willingness of other close allies to co-operate on similar matters in the future).

Then again, the current administration doesn't seem to have much love for its traditional allies, but lots of love for the almighty dollar so who knows what will happen.