So we can get high in public but not drunk...that seems odd.
Not necessarily. The interpretation of the law will be subject to debate, as the regulation makes no mention of drunkenness to my knowledge. Rather, it is against the law to be intoxicated in a public place, and there is no definition of intoxication. It is assumed that this obviously refers to alcohol, but now the courts will have to decide whether the effects of marijuana also qualify as intoxication. I say yes.
It is entirely possible to smoke or consume cannabis without becoming mind-numbingly high, just as it is possible to consume liquor without becoming black-out drunk. It's that grey area of "I only had one marijuana cigarette, officer," that will be tested in the courts soon enough.
And for the record, consumption of liquor in public shouldn't be illegal in my mind. Montreal seems to be doing OK with it.