We will only be flying somewhere start of July.
I was looking into this now as AC was offering 50pct discounts.

It's a 1-way southbound, Canade to US.

I prefer flying to taking Amtrak or Bus. I want to spend the least possible time on transportation.

NYC airport: not really a preference. I almost always fly from JFK but that shouldn't be a reason to avoid Porter.
I will drop off a Rental Car in Toronto. This seems to be possible both on Pearson and Island airports.