DO NOT pour hot water on the door. The second it hits the glass, it will shatter. Then you are really SOL. You can try lukewarm water, but if it doesn't work, then it will freeze shut even more. Try the sun idea, or see if you can park it someplace warm for a little while, long enough it will come unthawed and you can put silicone spray on it. With all the bashing on the door in the cold... just to warn ya... when it finally does come off, it is going to rip the weather stripping off, and that won't go back on without being warmed up.
Good luck.
