Okay, I'm recuperating from surgery, and maybe not firing on all cylinders and being a bit facetious here as a result, but "legalizing" cannabis was a significant contributor to his 2015 election win. An election promise, no matter how sensible or outlandish, need not be kept after you win. Decriminalization of some Schedule 1 substances has been brought up before by both Teams Red and Orange.
To answer your question, probably not many, as the most drug afflicted ridings are already red. My comment, though, was more aimed at the increased policing challenges associated with more legalization/decriminalization.
Casual users and dealers vote. I'll concede that cannabis is a different drug, but he sold it well and he garnered a lot of the 18 to 40 year old vote in 2015. Then, he then went on to legislate the crap out of it, so it's not truly "legalized".