well chanvre would be hemp, which is a product of cannabis, but is legal--it can be made into clothing among other things....
as for the companionship part, I need to know more context of the dialogue, because saying you have a companionship with hemp sounds odd. It obviously implies that you work with it.
I'd say off the bat if you were to use it in the first person, it would be: "I work with hemp"
that implies that you work with pot, but does not reveal that you are a dealer. it would be a sort of "covert" way of letting someone know if you sell pot. you can't get in trouble for hemp, so it's a safe method of telling.
I think that in this story, the man doesn't want to be clear with his method to earn money. He prefers to say Hemp than Weed, but he knows well that it's a seller of weed, am i clear?? Sorry for my low level of english!!