I'm just going to throw this out there....it's a bit more of a theory than anything that I can support by fact.
In the US, money talks. I think we all understand that the idea of taxing pot for revenue, but the big win is reducing the (imo, just ridiculous) amount of money spent policing, convicting, and ultimately incarcerating massive numbers of people for simple possession. At a rate of ~
$30,000 per person per year, States spend a huge amount of money locking people up. The prisons are bursting at the seams and most States are desperate to reduce the cost burden.
While there's certainly been some (surprisingly well organized) social pressure/lobbying to legalize marijuana in the US, I believe that the biggest reason it receives State Government support is based on the finances.
Lower policing and prison costs on one side of the ledger, and higher revenues on the other side. IMO, that is what's driving legalization efforts south of the border.
Comparatively, I don't think Canada (currently) sees the same level of pressure. That said, there's still savings to be had and for some reason we're trying to increase our incarceration rate despite the US clearly demonstrating that its a road to failure (although that's a different topic for another day).