Not sure how good that strategy will pay off with cannabis, though. There might be simple protocols which 'accidentally' work on cannabis too but what do you do with a doubled haploid then? It will most likely be a fragile, sick, weak, crippled runt whose only sense in life is being a homozygous carrier of a valuable and/or new mutation which will only come into play once outcrossed. To me right now (I admit, it's been a long day for me) it seems less trouble (and certainly more fun) to create a doubled haploid just because you can than all the crossing with other doubled haploids needed to find the real goal, a 'perfect' F1. Without genetic markers, the value of a DH especially in outcrossing species seems rather low to me.
I was reading into that subject a while back and there's a bunch of feasible strategies for certain crops. Most often, it's a freak of nature or a coincidence which creates and/or rescues the haploids of a given plant species (for example wide crossing in barley or tobacco: doesn't work so far with cannabis x hops, or does it?). Colchicine and IIRC also caffeine are used in the second step where you double the chromosomes. You should probably focus on gyno- and especially androgenesis
. If I can re-find those papers again, I'll let you know.