Get an undergraduate degree. It used to be the case that exceptional students could be admitted directly into law school, but this practice is becoming extremely uncommon. It persists to some extent in Quebec, where some students are admitted to civil law programs after finishing Collège d'enseignement général et professionnel.
Take the LSAT. Most law schools require it, so find out if the ones you are interested in fall into this category.
Finish law school. Provincially regulated bar associations require that candidates have law school degrees in order to join. A law degree from a foreign school may be acceptable, but bar associations may also require that such candidates submit to further education and/or testing.
Write and pass the bar exam. Each province has its own bar association, which in turn administers its own tests for bar admission. The Canadian Bar Association is an organization that works on behalf of lawyers and other bar associations, but does not administer licenses to practice law.