While DC is great for offering opportunities to US citizens, opportunities are rather limited for internationals. Many jobs are either with the Fed or companies mostly feeding on Federal contracts. They almost always require US citizenship and some even require security clearances.
The Kellogg certificate programs at Northwestern will offer the most advanced coursework along with the highest ranked economics department among the US colleges on your list (don’t know much about the Canadian system). If rigor and advanced coursework are what you are after, Northwestern is probably the best choice out of the US ones. Kellogg also has a 10-mo MS in management studies program only available to NU undergrads to apply.