Three countries: the United States, Canada and Mexico. Nothing else is included. If your route touches Guatemala, Belize, Cuba, Jamaica or any Caribbean island, the plan stops working the moment you cross that border, and no warning appears first.
Geography puts Central America, the Caribbean and Greenland inside North America. Mobile operators draw the line somewhere else. This plan uses the operator definition, which is the three big mainland markets and nothing south of Mexico. Panama, Costa Rica and Cuba are not on it. Our Latin America and Caribbean regional pages each list their own country count, so check yours there rather than assuming.
The reverse question is the one worth asking. Do not ask whether North America is covered. Ask whether Belize is. Write your itinerary out country by country, then match each line against the three. US territories are worth a message to support before you buy, because a plan sold for the United States does not automatically reach Puerto Rico or Guam.