Technically, they are on their own soil, so no, they don't have to fly our flag. Just as our embassies don't fly their flag.
That would be the Secretary of State, currently Hillary Clinton.
I think you can find your answer here http://en.wikipedia.org/wiki/Foreign_policy_of_the_United_States In the United States, there are three types of treaty-related law: * Congressional-executive...
Mexico and Canada
Ambassador.