Do you think it is better for Porter to fly to US airports that have good connection possibilities or to ones that are smaller and closer to downtown? (EDIT: I would include Canada in the discussion, but for the most part there is only one real choice for airports in most Canadian cities -- St. Hubert, maybe? Gatineau?)
For example:
Cleveland Hopkins airport (CLE) vs Burke Lakefront (BKL)
Cincinnati International (CVG) vs Cincinnati Municipal Lunken (LUK)
Minneapolis (MSP) vs St. Paul Downtown (STP)
Detroit Metro airport (DTW) vs. Detroit City Airport (DET)
Are there others?
(I would have included New York and Washington in the discussion, but in both cases, the close-in airports are "real" airports that also offer connection possibilities and are obvious choices if access can be achieved.)
The smaller airports generally have few, if any, connection possibilities but are generally closer to the city (which might be more convenient for travellers that are not connecting to somewhere else).
Smaller airports are very often cheaper to land and park at and have fewer delays due to congestion. They often do not, however, have advanced terminals with jetways, etc.
Flights from YTZ to smaller less-served airports will also compete less directly with YYZ flights (both end points would be different).
Of course, this almost certainly would have to wait until US preclearance is put in place at the island, since the smaller airports generally have limited or no customs facilities.
Personally, I would vote for the smaller airports as they are generally involve much less hassle and when I go to cities, I am generally going to the downtown core.
EDIT: with the quick turnaround possible at small airports, it might be worth stopping at more than one on each trip. For example, YTZ-BKL-DET-YTZ. If you only refuel at one of them (can a Q400 from the island do Cleveland, Detroit and back without refueling?), it wouldn't add to much time to stop at the other without refueling -- just unload and load passengers quickly and move on).
There is no reason why they couldn't do multiple airports in the same city if the traffic was there -- either separate YTZ-CLE and YTZ-BKL trips (one of them likely more often than the other), for example, or even perhaps YTZ-CLE-BKL-YTZ)