International flights are governed by treaties and international law and governments must grant permission for a foreign airline to land in their country. IATA tends to be a clearing house for a lot of this as they are part of the United Nations but in reality it depends on the treaty between the two countries. If open skies exist ie between the United States and Canada as a general rule all the airline needs is to aquire facilities at the airports, hire staff etc etc and IIRC file some basic paperwork with the two governments. Hope this helps some.