I am not sure I would do this but I follow an Ontario
Disney travel agent on Insta (claire_magicaldreamjourneys) and she has posted the idea of taking the train to Sanford from Buffalo and then driving her car the 30 minutes to WDW. I don't know how much this costs compared to driving yourself or flying but it is interesting option that I had never considered.
The Auto Train only runs from Lorton, VA to Sanford, FL., so you (that's a general "you") would have to drive from Buffalo to Lorton to get on the train. We live near Philadelphia and know a lot of families who have taken the Auto Train to FL and love it. Our family is not one of them. We have 5 kids -- all adults now -- but when they were younger, it was way more expensive to take the Auto Train than to drive the entire way. The cost just for 6 or 7 seats (depending on how many of us were traveling to Disney) on the train plus the cost for the vehicle was over $1,200. If we wanted a room with beds, it was significantly more expensive. Our gas, food, and hotel rooms were closer to $800 roundtrip. The train leaves Lorton at 5:00 p.m., but check-in is 12:30-3:00 p.m. Arrival in Sanford is around 10:00 a.m. but you still have to wait for the cars to be unloaded before you can start the drive to Disney World.
I've often compared our "average" driving trip (we've driven 10 times) with our friends "average" trip on the AutoTrain (they've done it 4 times). We live 2 miles apart from each other at home, so distance wise, everything is the same (it's a little more than a 1,000 mile drive). We would leave our house at 5:00 a.m. to start the drive to Disney. We'd stop for lunch and several bathroom/stretch breaks along the way. We'd stop at hotel for the night by about 7:00 p.m. and get dinner close by. We'd shower and get a good night's sleep and hit the road by about 8:00 the next morning. We'd be at Disney and in our room before noon (usually earlier). Our friends would leave their house by about 9:00 (it's a 3.5 hour drive to the train station). They'd check in as soon as they arrived and then walk somewhere to have lunch. After lunch they'd have 3 hours to waste before boarding the train. The train would depart at 5:00 and arrive in Sanford around 10:00 (they've gotten in as early as 9:30 and as late as 11:00). They spend the night sleeping in their reclining seats. Once their car is unloaded (one time it was the very last car unloaded) they have about a 1 hour drive to Disney World arriving around noon.
So, to compare, they leave the house about 4 hours after we do but arrive at Disney at about the same time. The *big* difference for us is that we slept 8 hours in a nice comfy bed (not a train seat) and had a nice hot shower. We arrive at Disney well rested, refreshed, and ready to go. They've often arrived at Disney and immediately taken a nap because they didn't sleep well on the train. They've also had disappointing food and issues with the bathrooms on some trips. The other big thing for us is that the drive from our house to Lorton, VA is the absolute worst part of the drive due to traffic. After Lorton, we need to get through Richmond, VA and then it's clear sailing and an easy drive (no cities to get through or around -- just a straight highway) until we get to Jacksonville, FL.
I know a lot of people swear by the Auto Train because they don't like to do all that driving. The Auto Train is a great option for people in that situation. While we know plenty of people who love the Auto Train, we also know a few who had such a bad experience on it that they will never use it again. My husband doesn't mind doing the drive, so we probably won't ever take the Auto Train though I won't rule it out for when we're older or if I had to do the driving myself. It just won't ever be our preferred method of travel.