I think use of cannabis will increase in Canada after legalisation and I doubt anybody will disagree or project a decrease. I think a bigger question is whether public opinion will continue to trend favourably in light of current medical knowledge which seems to think that cannabis causes less harm than alcohol thus making it a better way to waste time and/or ease general existential angst on the weekends.

While I don't think more people getting stoned is necessarily 'win' for Canadian society, I think if it diverts them from other more harmful forms of impairment (alcohol or 'hard' drugs) it probably is.