If people do not drive, carpool or bike to work, they either walk or take public transportation. Generally, public transit is run by the municipality, city, or town. In larger cities with a lot of commuters, there may also be provincially-run transit such as the GO trains and buses in the Toronto area.
In most towns and cities, public transit means buses. Some cities also operate ferries, streetcars, and/or a metro, subway (underground) or elevated train system.
Here are links to public transit information in many of Canada's provincial and territorial capitals and other major cities:
Commuter trains and buses also run between suburbs and the downtown areas of major cities including Montréal, Toronto and many cities in British Columbia, http://www.westcoastexpress.com/main.htm, etc.