Where does cannabis come from is a great question. The answer to this question depends on where you live. Cannabis can come from your backyard, down the road, around the corner, across the street, the state next to you, the other side of the country or even from around the world. If this makes any sense to you then you understand that cannabis is not something that is regionally grown in one area but it is everywhere. Cannabis comes from tropical climates in South America all the way to colder frigid climates up in countries like Norway. Cannabis even grows in the frigid mountains of Afghanistan and Pakistan.
On a similar note when you ask where does cannabis come from many times it just comes from a dealer. A grower and breeder will grow marijuana. Trimmers will trim the buds and prepare them for consumers. They are then handed off to dealers which sell them to the consumers looking to buy marijuana. In an essence, marijuana comes from the ground. If you are one who follows the Bible Genesis states that marijuana was given to us by God.
Genesis 1:12 "I have given you all the seed bearing herbs and plants to use."
If you are not one that is religious then it is undeniably a fact that marijuana comes from a seed that grows in the ground. It is not synthetically engineered in some fancy medical laboratory or bathtub chemists basement laboratory, it grows naturally. The answer to the question where does marijuana come from depends on the depth of the answer you are looking for. Are you wanting to know where to get it or are you wanting to know how it came to be? If you're wanting to know how it came to be there will always be that debate the "Which came first the chicken or the egg?" question except it is, "which came first? The pot plant or the seed?"