We are flying direct on WJ in April, Wed-Wed flights. This may not be an option in the fall though. If you *have* to connect, my personal preference would be via Montreal just because I find the airport slightly more compact than Toronto. But ultimately connecting via YYZ, YOW or YUL is going to be about the same amount of time, give or take an hour.
I would take Montreal over Toronto, but definitely Ottawa over either, hands-down. Ottawa airport is comparable in size to Halifax, and customs is easy since the number of international flights is quite limited.
That said, there aren't a lot of direct flights from Ottawa to Orlando, so flying through Ottawa might not even be a viable option.
My mother is flying YOW<->MCO direct on Air Transat next month, and the price wasn't crazy, but that route is probably seasonal. And the outbound flight was very early.
If OP connects in the US on the return trip, it will be considered a domestic flight for the purposes of
MDE, which means a pick-up time 3h in advance of your flight instead of 4h in advance. There are varying opinions on whether or not that should be considered a Good Thing.
Agree with PP that Google Flights is your friend. Unless you're flying over a holiday (Thanksgiving?), it's probably too early to get the best prices now. Keep an eye on the dates you're interested in, and book when you see a price you can live with. Keep in mind that prices *will* change, usually in both directions.