How to get to Niagara Falls (Canada side) from Toronto airport during a layover?

TL;DR: Try go catch the 8:20 Via Rail from Union Station to Niagara Falls, arriving 10:16, if it runs on your day. If not, public transportation is going to be very time-consuming but possible.

It's quite possible to get from Toronto Pearson via Union Station to Niagara Falls, but you won't have a lot of time left to spend there. The cheapest way to get from Toronto Pearson to central Toronto (Union Station) is by TTC, with the Airport Rocket followed by metro. This will take more than an hour and costs 3.25$ each way. If you are in a hurry, you can take the Union Pearson Express which only takes 25 minutes and costs 12$ each way, faster and cheaper than a taxi. From there you can take GO Transit (train+bus), VIA Rail (train, seasonal, once per day) or Greyhound (bus).

Intermezzo: Warning: Do not expect European quality public transportation in almost any North American city, and certainly not outside of them. Even between cities, public transportation in southern Ontario is incredibly poor¹. This is not Paris, London, or Berlin. Trains within Toronto are poor, suburban trains in the region around Toronto are extremely bad, in particular on weekends. For example: Kitchener (500k inh.) to Toronto (2.7 million), 100 km, has 4 trains/day, weekdays only, taking 2 hours (bus takes 3); Oxford (170k inh.) to London (8.7 million), 95 km, has 72 trains/day, taking less than 1 hour. The Scottish Highlands have more frequent trains than cities near Toronto.

^{(It's the main reason why I left Toronto; my driving skills suffice to pass the test in The Netherlands, not so in Toronto, so I was essentially stuck; I did carpool out of the city a couple of times; once it took 3 hours in traffic to get out 60 km from the city centre; I also remember being stuck in traffic with a bus, 100 km out of Toronto, midnight after a Bank Holiday weekend.)}

Still reading after the intermezzo?

GO Transit operates trains and buses between Toronto and Niagara Falls: see timetable. There are many services per day. It will take roughly an hour to reach Burlington, where you change from train to bus, then it's another 1 hour 35 minutes by bus. Depending on your connection, it will take almost 3 hours from central Toronto to Niagara Falls, excluding delays. Price for a day pass is $37.50.

There is also, at most 1 train per day run by VIA Rail. I think it runs seasonally. When it does run, it departs 8:20 from Union Station, arriving 10:16. As far as public transportation goes, it is your best bet, assuming you can make it and it runs on the day of your transit, that's probably the most comfortable option. The return is too late for your flight, though.

If you have some time left after awe-ing at the falls, I recommend a hike in the Niagara Glen nature reserve, peace and quiet just a stone throw away from the Ripley-Believe-It-Or-Not-esque tourist madness that is Niagara Falls as soon as you turn around and face the town rather than the falls. There's also a really nice butterfly garden. Churchill said that the road between Niagara-on-the-Lake and Niagara Falls was the most beautiful one in the world but he was mad and/or liked wine too much. It's nice but not most-beautiful-in-the-world-nice. If you're driving anyway, Niagara-on-the-Lake is probably worth the detour.

If you choose to drive, make sure you are comfortable driving on the rather huge and congested roads in the Toronto area, although the airport is west of town so you will avoid the worst part of the 401 (which has up to 17 lanes).

¹Apparently, there are similar-sized cities where it's even worse, but I have no firsthand experience of those.

I'd recommend the Niagara Air Bus! My parents lived near Niagara Falls and I used to take it there and back. They run hourly I believe. They used to drop my off and pick me at my parent's front door so you'd certainly get dropped off and picked up at a convenient location. Best thing about them they're savy about getting you to the airport in time for your flight. Also quite comfortable and I'm tall. You can book ahead so it's all set up when you arrive.

I live roughly half-way between Pearson Airport and Niagara Falls, and warn you that traffic will likely be horrendous. Although the drive is only 1:45 in light traffic, you will be driving both directions in rush hour, and that will be the likes you have rarely seen before. Allow 3 hours for your return drive, so leave Niagara Falls by 1:30 or risk the chance of missing your flight.

Note that for part of the highway, both directions, there is a High Occupancy Vehicle (HOT) lane along the leftmost side. Outside of Toronto proper it is sufficient to have 2 people in the car to qualify, even though inside the city there must be 3 or more.

If you opt for the GO train service, I recommend driving to Oakville Station and parking your rental car there; it is likely the closest station at which you will find free parking available by the middle of the morning Rush, and is only 3 minutes off the highway. Heading downtown to Union Station will simply lengthen your commute to Niagara Falls to no purpose.

That being said, you will enjoy the Falls and can expect to have around 3 to 3.5 hours to enjoy them, in the best time of the day.

I did this a few years ago. Clearly, rent an economy-sized car at the airport and just drive there. It took 1hr to 1hr 30min to complete the trip in one direction, in a situation where there was no significant traffic.

Navigating the roads is really easy. Leaving from the airport you quickly reach the interchange that connects you to the QEW freeway, then you drive it on nearly its entire length before switching to a short feeder freeway leading you to the Niagara Falls town; direction is written on sign at that point. Parking in Niagara Falls can be a bit challenging in high season, though.

In Niagara Falls town, there is a lot to do. In addition to riding the boats dressed up in rain coat (provided), you will be able to enjoy the Vegas-like downtown with some attractions including an observation tower. At the time I went there, I expected to be greeted in a kind of natural site or national park setting and was surprised.

I visited Niagra Falls while on a 2 week holiday in Toronto, and both the girlfriend and I drove from Toronto to Niagra. It's really the only way. It looks like it's no distance at all on a map, but you then realise you have to drive around the bit of water that's between Toronto and Niagra.

As the others have said, rent a car, and leave plenty of time to drive there and get back. Traffic can be bad, it was for us when we came back to Toronto. Not entirely sure what time this was though.

To repeat what another person has said, the Canadian side is better than the US side (Sorry!), and definitely take the Maid of the Mist tour. It's magical sailing right up to the wash of the falls.

Depending what you like, the town itself is a bit like Las Vegas. I've never been to LV, so can't compare, but it did strike me a lot like Blackpool. Very tacky, loud etc. Not entirely befitting of the natural wonder you're after, but that's my opinion.

But, 30 mins outside of Niagara Falls is a town called Niagara on the Lake. It's beautiful!!!! The buildings are brilliant, the pace of life is so quiet. We were told to go there by a resident of Toronto after I got caught on camera as they filmed some sort of candid camera show. 100% would recommend you go there, even for an hour. You won't be sorry.