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On long haul flights, US to Europe for example, most airlines offer lie flat business class.
But on a flight from say NYC to Toronto (or LA to Mexico City), those are international flights but because it is a short flight, they might not have lie flat business class.
Basically you have to check every time when you book the ticket.
There is typically a seat map when you pick your seat and it should tell you if it is true lie flat or not.