Hello Bruce,
First and foremost,
Disney's Yuletide Fantasy tour is on my Walt Disney World bucket list and I can only imagine the amazement you will experience when discovering the hidden gems of how Walt Disney World brings the holiday magic to its entire resort.
Typically, yes, you are able to take a leisurely stroll and enter through the International Gateway entrance and make your way to the front entrance of Epcot. However, your dilemma is you need to be there by 8:45 a.m. and if Epcot does not have an Extra Magic Hour that morning, then it will not open to Guests until 9:00 a.m. Your best and quickest option, then, is to take a taxi. If you use Disney bus transportation, then allow yourself about an hour travel time. You will need to board a bus to Disney's Animal Kingdom theme park and transfer to an Epcot bus. As you know, 15 minutes prior to the tour, you will meet at the silver and blue, "EPCOT GUIDED TOURS MEETING LOCATION" sign, located to the far right of the Epcot main entrance.
I hope this is helpful in deciding your best option and if I can be of any further pixie dusted assistance feel free to ask and enjoy discovering and experiencing the many magical and memorable holiday wonders of Walt Disney World.
Amy M*o*