note UA doesn’t fly RDU-YYZ nonstop, so if you really wanted to go to UA metal for front cabin, you’d need to do RDU-IAD/EWR/ORD-YYZ, and then onward. For a, what, 2 hour segment like that on the way to Japan, where there is already an extra segment after that, not so sure I’d opt to add a connection point (also: one more place where things can go wrong) to get a domestic F seat.