It does depend on your final approach. As a Central Florida local who's family lives across the country, I've flown in from the North, South and East as my final approach. I can typically spot the majors when I'm either flying out or landing, I can find where SeaWorld, DW, and Universal are, as I know right abouts where they should be.
If you are not fimilar with the area, seeing WDW from a plane would be very difficult. Several times I've pointed to my boyfriend saying, "we're flying over MK right now" and I'll point right to it, but he still can't see it.
So really, there's no garutee that even if you are on the correct side fo the plane and do fly over WDW, that you'll be able to spot it. But there really isn't anyway to know what side of the plane to sit on to see it.