Most recognized & most prestigious probably depends upon your area of study as all are very prestigious schools.
Because you want to study business and international relations, McGill & Georgetown should be your top two unless you prefer New York City.
Northwestern does not offer an undergraduate business degree,however, economics is an outstanding option at NU and certificates from Kellogg are available.
My impression is that the study of business is your primary interest or else you would have targeted Georgetown’s School of Foreign Service.
Can one major in both business & IR at McGill ? If so, then that option should receive strong consideration.
Interesting locations = Montreal, Chicago, Los Angeles, New York City and Washington DC.
P.S. With respect to which school would “open the most doors”, it depends upon where & for what type of opportunities.