Toronto Pearson International Airport: 
is about 30;50 minutes by car from the downtown core and is serviced by most major international carriers. There are two terminals: Terminal 1 hosts all Air Canada flights and a few other international  carriers while Terminal 3 hosts all other airlines.
There is no direct passenger rail link from the airport, but other options do exist for getting downtown from Pearson.
TTC provides public bus services that run to and from Pearson. The best TTC option is the 192 Airport Rocket that runs every 10;30 minutes between Kipling Station on the Bloor Danforth subway line and Pearson Airport. Kipling Station is the westernmost subway stop on the Bloor Danforth line and it takes 1;1.5 hours to reach downtown. One way adult fare on the TTC is $3.00 which includes free transfers to other TTC buses or the subway. Tickets can be purchased from the Bureau de Change in Arrivals. When the subways stop running at around 1:30 AM, the 300A Bloor Danforth night bus provides service along the subway line and goes directly to the airport.
GO Transit  provides express buses to locations outside of Toronto's downtown. It operates from the airport to Yorkdale and York Mills subway stations in North York every 30;60 minutes for $4.05. This takes about 35-45 minutes, followed by another 20 minutes on the subway to get downtown (one must pay a separate fare to board the subway; $3.00). A new GO Transit service offers service to/from the airport to Richmond Hill Centre . This bus service runs every 60 minutes from about 5:00AM to 1:00AM daily. The GO Bus Transit service between Square One and the airport no longer operates. Alternatively, Mississauga Transit  provides service options between Square One and the airport.
Pacific Western Airport Express operates a quick, convenient, and frequent bus service .It picks up passengers at both terminals, and stops at several major hotels in the downtown core, as well as Union Station and the inter-city bus terminal at Bay and Dundas. Adult fares are $19.95 one way, $32.95 for round trips. There is a 10% discount for online reservations.
Taxis run a flat rate of $40, while airport limousines go slightly higher at $50;70. Limousines are generally slightly larger  and more comfortable vehicles than taxis. Government approved rates can be found online.
Toronto City Centre Airport: 
handles short haul regional flights only. Its main tenant is Porter Airlines, a low cost carrier that operates flights using turboprop planes to many cities in eastern Canada and the northeast United States (Boston, Chicago, New York/Newark and Myrtle Beach). One of the main benefits of flying into this airport is its proximity to the downtown core. Upon landing, you can be downtown within ten minutes.
A free ferry service makes the short crossing between TCCA and the mainland every 15 minutes, 6:45AM;10:07PM. Once on the mainland, a free shuttle bus connects the terminal with Union Station.
Hamilton International Airport:
located about 80 km from downtown Toronto and Niagara Falls, is served by WestJet and Air Transat. This airport is not served by public transportation, but you can take a $25 taxi ride to the Hamilton GO Station (36 Hunter Street East) in downtown Hamilton, where you can catch a GO commuter bus to Union Station in downtown Toronto ($9 one;way). Buses run every 30 minutes.
For frugal travellers coming from the United States, Buffalo Niagara International Airport (IATA: BUF)  is another option, as flights to Buffalo tend to be significantly cheaper than to Pearson. Megabus  runs from the Buffalo Airport to Toronto; the trip takes 3 hours. Rental cars are available at the airport if you prefer to do the drive yourself. Buffalo Airport Limo offers a flat rate of $175 to downtown Toronto from BUF.