What you will be able to see is the fireworks that are shot into the air. You cannot see what is happening at water level at World Showcase from any the boardwalk view rooms, GVs included. View is good from any but somewhat better as you move down the boardwalk. There are no GVs near Jellyrolls, The last one going down the boardwalk is still over the main store and before the Big River Grille. Also be aware that you can see the upper fireworks at MK looking out over the Yacht Club.