As long as you are below the weight limit you can go. In no place is Porter bound to only fly within 500 miles. You can carry less passengers, by not opening all the seats for sale, limit luggage as they did for direct flights to Halifax, or have a fuel stop. The flight to Toronto could be non-stop since your operating from a longer runway, and if you judiciously manage weight and fuel they can make it the other way on most days, perhaps excepting +30'C days.

Kyle