Meanwhile in Canada a drunk driver can't be fired from her job driving company vehicles because alcoholism is a disability.

That sounds illegal to me - You might contact a lawyer who deals with Federal Disability law. I think your case falls under that.

You should speak to an employment lawyer. They typically provide a free consultation, to determine if you have a case. For example, just because it’s in the rule book doesn’t mean it’s actually enforceable

I would be shocked that this actually is legal. Do they also fire all women who are on birth control pills? What about heart medication, blood pressure medication, or anti inflammatories (Aleve, Advil, Tylenol)? I take prednisone and cymbalta for adrenal gland failure, would I not be allowed to work there? And while we’re at it, caffeine is the most commonly ingested drug worldwide. Don’t suppose there’s a ban on soda and coffee at your workplace. When a company has a ‘no drug’ policy, that’s supposed to mean controlled substances that are obtained through illegal or nefarious means (ie: not through a doctor and given by a registered pharmacist!).

that's complete bullshit. if it was a good job, sue the crap out of them. no matter what, you need to get unemployment and definitely get a consult from a lawyer. that is definitely grounds for a case.

I’m pretty sure that’s illegal - look into it

That's a lawsuit. Get an attorney. Slam-dunk case.