That may not work for several reasons. First of all the largest number of users are under the legal age to drink. I doubt that they would be allowed MJ instead. Second, taxing it would make it expensive. Who would pay for taxed MJ when they could get untaxed MJ for a lower price? Third, legalizing MJ would add one more legal drug that would be freely available to Canadians. Given that legal drugs are the biggest problem
Canada has that might not be the best idea.
For a lot of folks, most of the enjoyment comes in getting away with something. For them, when the thrill is gone, so are they.
Taxes would be considerably less an additional cost than dealer mark-up added to the hospitalization costs to counter the stuff they rub in to make it go farther.
Decriminalization, regulation and availability would kill all those profits that attract organized criminals - thus eliminating much need for end users to commit crimes in order to generate funds.
Addiction is a medical issue ... not a legal one.