National College of Aviation

To be a private pilot (of small planes, single engine, single crew, day only, clear meter only, etc), you need to be at least 17 y.o., have a medical certificate, pass the radio exam, pass the theoric exam (includes aviation laws, navigation, meteo, how a plane works and flies, etc), have at least 50 hours of in-flight experience (including a cross-country flight, solo flights, etc), and pass the flight test (with an examiner of Transport Canada).
Then, if you want to go professional (and actually get paid for flying), you need the Commercial pilot licence. It requires the previous licence (Private pilot), another 50 hours of experience and additional qualification that you must pick up after the private pilot licence and before applying for the exams for the commercial one. These qualifications include stuff light night flight and flight by the instrument (for example when you're in a fog and depend solely on your instrument). The medical certificate required is also more restrictive.
After getting the commercial pilot licence, you can get paid to fly small planes with 1 to 3 passengers. You need to get an additional qualification to move onto bigger planes, which might require more flight experience. Pilots of big airliners, like B747 or A320, have thousands of hours of experience in flight.
Each step mentioned here is increasingly expensive, so you'll usually manage to do all that by being paid to fly, once you get your commercial licence. But before getting the commercial licence, you'll need training for both theory and practice, which will have to be assumed by yourself. In Quebec, there's a public school (the CQFA, which is a Cgep, so where tuition fees are mostly paid by the government) that offers the formation up to the commercial licence, but it is very hard to get admitted. You can also try the military, or (if you're 12 y.o.) enrol into the Canadian Air Cadets, spend 45 years there and apply to be one of the few in the country to receive a free private pilot formation. Some company in the aerospace industry will encourage you by offering to cover some few fees.
I also heard that other countries have different requirements and path to get the formation. For example, I heard cases where people got their licence while studying (aerospace) engineering in France because their school was encouraging it and was covering a lot of the fees for the formation.