Flying into Toronto (the airport is actually in Mississauga, but it's all one big urban sprawl) is interesting. That part of the province of Ontario along the Great Lakes is very flat and mostly rural if you approach from the north. All of a sudden, you're over civilization as you descend to the airport. There are suburban neighbourhoods dotted with bright blue pools at nearly every house. There are chunky blocks of tall buildings in the distance by the edge of Lake Ontario, downtown Toronto and more chunky blocks as you move out towards the 401 highway periodically. If you're at the right angle and on the right side of the plane you can see the slender CN Tower rise above it all in the distance as well. On the negative side, sometimes you can really see the smog like a blanket over it all. I have seen that a few times too though arriving in Toronto fairly early one morning, the glow of the sunrise lit it all to gold.
The Lester B Pearson airport is not my favourite airport nor is it most peoples'. Even though they've done some major renovations, it still tends to be rather soulless and a bit of a nightmare to find your way around. There is a skytrain that connects the two main terminals. The passport control for international arrivals is a bit like a warehouse. If you have to recheck your bags, it's just a tiny little area and then it's a long walk to the terminal where you need to catch your connecting flight. For all the renovations they've done, there's still very little shopping available behind the security checkin. There are a couple of restaurants/bars and a small number of souvenir kiosks and convenience type shops. For all that Heathrow is also a nightmare, at least there's lots of good shopping to kill the time.
To get into the city of Toronto, the airport bus is probably your best bet. There are stops at many of the major hotels downtown and one in Yorkville. You can get off at the stop at Union train station and take the subway from there. A taxi into the city will be expensive, it always is. There are several public bus systems available as well going in various directions in addition to downtown Toronto.
Once you're downtown, the subway is very easy to use. There are only two lines, one making a U-shape with the bottom of the U at Union Station right on the lake shore and one that crosses the middle of the city by Bloor Street. Toronto also has an extensive bus network and still has some streetcars as well. You can get a day pass or a weekly pass, a monthly Metropass (but any of these will cost you a little extra for a trip on an express route). All passes cover all modes of transportation on the Toronto Transit Commission (TTC). Cash fare for an adult is $3.00 and you can buy 3 or 7 tokens for an adult, 5 or 10 tickets for a senior or 10 tickets for a child. The TTC's website has all the information, maps and schedules. http://www.ttc.ca/