Public Transit in Ontario varies.
The most 'sophisticated' transit system is in Toronto, but absolutely any Torontonian will tell you: it sucks...bad.
The subway only has 3 lines. For the rest of the city you need to take a bus or streetcar (like a tram). The subway closes at 1:20 am every day and on Sundays doesn't even begin running till 9 am (inexcusable in a place like this). There are 24 hour bus routes but they don't come often and therefore tend to be absolutely packed.
Here's a pic of a TTC Streetcar...
*Side note* If our current mayor has his way, the funding for the TTC (Toronto Transit Commission) will be cut further and will suck even more. :(
A day doesn't go by where the subway doesn't stop either for medical, criminal, or mechanical reasons.
The buses are extremely unreliable in that they are rarely on point with the schedule. The streetcars are better...but still hardly reliable.
In the heart of the city there are lines where the streetcars or buses come much more frequently than on the lines that are out of the downtown core.
For someone travelling across the city (which is many, many people) you would have to transfer generally at least 2 or three times (which in the winter, can be a real bi*ch).
For the rest of Ontario, there are the GO Trains which go around the GTA (Greater Toronto Area-meaning the suburbs and less important cities within an hour or two distance) and then there are other options to get further away, which are generally the same as getting anywhere else in Canada.
You can take the VIA Rail, which is the train, that has trains going all over the country.
There's Greyhound Bus, MegaBus and Coach Canada, which go from the main cities several times a day and, if booked in advance online, can be quite cheap.
There's Porter Airlines, which is a wee tiny airline that only operates from certain cities within Canada and the US and tends to be cheaper, and is nice because it is located right in downtown Toronto, instead of the suburbs like Pearson International.
For the smaller cities in Ontario, such as Ottawa, London, Waterloo, etc. there are generally local public transportation systems, but they operate, for the most part, less frequently, and for shorter hours, than does the public transportation system in Toronto.
We are quite "green" here though (ish). So, many people own cars BUT for people who either can't afford them or are too eco-conscious to buy them...they can join the many others in the province that somehow manage using only public transport.