We've driven down to WDW from Toronto 4 times in the past 2 years, but unfortunately, none of those trips were during the winter months (1 June, 2 Octobers/Novembers, and 1 April trip)... but we've always driven the QEW/I90/I79/US19/I77/I26/I95/I4 route through NY, PA, WV, VA, NC, SC, GA to FL. (Do you sense I can practically drive the route in my sleep?)
I can see where it could definitely be difficult during the winter through the mountains in WV and around Lake Erie (can you say "lake effect???") and I can certainly understand why CAA recommends the western "curve" route during that time of year. Yes, if Lakes Ontario & Erie weren't in the way, it'd be a straight shot south from Toronto!
Have you ever driven either route before yourself? If so, you might just feel more comfortable with the route you're more familiar with (I know that's how we would most likely decide, unless Mother Nature changed our minds at the last minute.)
Depending on how bad a winter North America has next year, you might not have any problems driving the mostly-straight route, and I imagine you'd probably save a bit in gas (although the drive through the mountains would probably burn more fuel than the "flats" would on I75. Of course, you could always plan the second route as your backup, just in case a major snowstorm hits in the days leading up to your trip. (If you're making reservations for stopovers, most hotels will allow you to cancel up until 4 or later in the afternoon of your check-in day, at least that's what we've found to be the norm.)
If you do decide to take the I75 route, definitely pick up the "Along I75" book, as Tracey suggested; (the guy who wrote it lives in Mississauga)... we bought both it and another book highlighting the 401 & I75 in case we ever take that route, but we like "Along I75" *SO* much better... the maps in the other book were in black and white, and there was advertising on every page, or so it seemed... the colour book is just so much easier to read and understand. (I keep thinking that I should write a similar map book for our normal route, but WOW the amount of time it would take for the research!)
I hope that this helps... if you haven't ever driven either route before, let me know and I can at least fill you in on what you can expect (stopovers, cities, stuff like that what to expect, as opposed to weather-wise!) along the route we normally take.
Good luck making up your mind!
Sandy (and Brian, Bonnie & Kellie!)
) just for a change of scenery. We've done I81/95 (2x) & the above route (2X) so that one would be a nice change. I love the drive to WDW...anyone want to drive down with me next time 
my van holds 7 
...oops...guess we need some room for luggage...well we could strap it on the roof and if someone ticks us off - exchange their place in the van with the luggage 
