Hi Annette!
Thanks so much for the kind words! We love hearing from great Guests like you!
It sounds like you're already an expert Disney planner. What a fabulous evening you've planned out!
Yes - you most certainly can choose to pop out and back into Magic Kingdom during Mickey's Very Merry Christmas Party if you'd prefer to view the Holiday Wishes Fireworks from atop the California Grill. Just be sure to hang onto your receipt from dinner to have your access to the rooftop overlook granted upon your return.
Holiday Wishes will be showing that evening at 9:30pm.
Be sure to also catch one of the two Mickey's Once Upon a Christmastime Parades which are at 8:15pm and 10:30pm. Another fabulous holiday event you won't want to miss is
The Magic, The Memories and You!, castle projection show. Check the Christmas Party Times Guide for multiple show times that evening. You'll want to secure a spot in the park, on the Main Street side of Cinderella Castle with a great view of the Castle for this spectacular show.
Thanks so much for choosing to visit me! I especially enjoy hearing from fellow Canadians and fellow Ontarians. I hope you'll visit me again soon with any more questions you may have!
Wishing you a simply Magical time during your Holiday visit to Walt Disney World Annette!
Kirsten