I assume, then, that the answer is the Canadian government chose to place the barriers there, probably at the request of the U.S. government. I agree with you about that particular site being an unfortunate choice. Historically, host nations always have had the right to accept or reject proposed embassy locations, and, in modern times, reserved the right to determine what security measures, if any, need be taken in consequence.
That said, I imagine that most neighbors of embassies all over the world think that some other site far, far away from their neighborhood would be infinitely more suitable. |