My home airport is YYZ, and if you can find a $300 fare for YYZ-NYC, I say take it ! I've rarely found fares for that low, with the exception of getting lucky on AC seat sales.
YYZ is one of the most expensive airports to fly into/out of, period. Add to that Air Canada's monopoly on so many routes, and it creates a funny-smelling situation.
What I have been doing recently is driving over to Buffalo and flying out from there. Last month, I saved $300 on a BUF-DCA vs YYZ-DCA route. Im flying again at the end of the month to save $200 for a BUF-JFK vs YYZ-JFK route.