Reality check time:
I guess the first question to ask is: which is more important - your ability to use mmj or your job.
Note that I did not ask which was correct, which was fair, or which was right.
The supervisor-wife above is correct. This company has rules, they like their rules, they live by their rules, and the rules are on their side. To top it off, they also have the provincial mining regulations on their side. From this day forward you will be under the eagle eye of HR for every little thing you do. Even if you win - or especially if you win.
It is possible to give up your mmj and return to work, while continuing a legal battle against the company. But it will be long and fraught. And in the end: what will you gain? You may gain a victory for yourself and other medical marijuana users, but you will be the one that pays the price.
As much as gains in this sphere require a number of people willing to step up and take one for the team, this is not something that can be advised in good conscience. Taking one for the team is usually extremely costly financially, emotionally, job-wise and family/relationship-wise.
Again: is it worth the price? Only you know the answer to that one.