I've flown between the USA and China several times, and each time it seems the route is at least slightly different. I've seen the Shanghai->Newark flight range

I've flown between the USA and China several times, and each time it seems the route is at least slightly different. I've seen the Shanghai->Newark flight range from directly over the north pole, then coming down over upstate NY; to going over Japan, just south of Alaska, and paralleling the Canadian border. So there's clearly not a single correct route. My neighbor at the time was a commercial pilot, and I asked him about the difference. He says that anything else that the airline or anybody else tells you ahead of time is only tentative. The final call on the route is made by the pilot on departure. He's considering things like wind speed and direction along the way, weather along the route, and weather at potential intermediate airports should an emergency arise. Bonus fact. He told me that he dislikes flying the newer Boeings because of the location of the cupholder. On other planes it's closer to the plane's major axis, but these planes put them farther away. This has the effect of magnifying the plane's motion, and leads to coffee spills.