Who reality cares who wants to install it?
Once the pipeline is installed on US soil, we effectively control it. The owners can not take it back, and in time of war it could be confiscated.
I don't know, but it has been suggested that the American portion of the pipeline would be owned by a US subsidiary of TransCanada. As for your war reference, as long as the oil flows there would be no reason for the US government to take over the pipeline. I don't anticipate a war between Canada and the US within the lifetime of this pipeline.