Your best bet for a good view is probably to head back to MK.
The view from GF is not centered, and you will be done with dinner way before the fireworks go off anyways (with a 5:15 you will probably be done by 7 at the latest).
The Poly's view is a better angle, but to get there via monorail you will have to ride the entire circuit - MK-Contemporary-TTC-Poly to get there. You'll get a more up-close-and-personal view if you get off at the MK stop.