On October 17th 2018 it became legal to smoke pot across all 10 provinces and 3 territories in Canada.
Some slight variations remain with respect to age limits and retail options, but in general it is now legal to smoke marijuana wherever it is legal to smoke tobacco and the purchasing age mirrors the legal age for purchasing alcohol.
That means that in Ontario a 19 year old can purchase marijuana, can carry up to 30 grams in public and can own up to four plants for the purposes of cultivation and home production.