I think I might book everyone's travel for Xmas now, and book his (probably at a higher price) once the exam schedule is listed. If his exams go to the 23rd, he'll fly out of Windsor. If he's off early, he'll fly with us from the GTA. That's probably the best I can do.
While it's none of my business, why did your DD choose U of S? It's a good school (yes, the exist outside of the East, lol), but I wondered if it was a particular program or scholarship or something like that? It is far away and not that easily accessible, even by air.
My niece chose a school in PEI over any in Ontario, where her family is, but she chose it because it was smaller class sizes and a better chance to be known by her teachers. She didn't want to be a number in a mega-school.