Definitely enjoy the weather while it's still here. I am confident that this will fix the ntdll Canada crash for you once and for all. According to the thread, restarting coatl+rebuilding airport cache after push has worked for some as well. For me, I shut it down completely in the task manager just to be safe.
This sounds like the infamous Northern Canada ntdll crash. I had issues with this one as well for awhile. Try this: after you get your pushback with GSX and have all engines running, go into your task manager and kill coatl.exe. You should then be able to make it across Northern Canada just fine every time. There was a thread in the P3D forums with a pretty extensive investigation into this one. This was the solution.