I won't get into specifics, but I was hired at a major Canadian dispatch center despite admitted cannabis use. And the admitted use was months ago, not years ago. However it also included period when it was illegal too, and I admitted that. Since starting the job a couple months back, I have interacted with several other call takers and dispatchers who similarly were honest about their use without issue.

They are concerned most with ties to organized crime, and are also screening for serious addition problems (which might make someone more susceptible to bribes, etc). Smoking a joint and watching Planet Earth once in a while isn't a problem. Drinking a couple beers during a hockey game isn't either.