Homegrown weed in a framework of legal marijuana sales will be a problem the same way homebrewed beer is a problem in a framework of legal beer sales, and homegrown tobacco is a problem in a framework of legal tobacco sales:  it won't be.

If you get invited to the right dinner parties you might be offered these things for free by your host, but there is essentially no "black market" in homemade alcohol or tobacco, despite their being totally legal in Canada, for a totally predictable reason - there's no reason for a demand to exist.