You would have to ask people from the industry for precise numbers and percentages. All we've been told is that 80% of flights between Europe and Canada in both directions do overfly the U.S., and we know that for all Latin American and Caribbean--
Evidence of meeting #36 for Transport, Infrastructure and Communities in the 40th Parliament, 3rd Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was information.
A recording is available from Parliament.