I know I'm late to the party here, but I'll throw my two cents in here. I'm in a fraternity, and I can confirm that stuff like this happens all the time. This isn't an isolated incident unique to Canada, unfortunately. It was so bad that at my university, a different fraternity (of whom many were my close friends) was falsely accused of some pretty disgusting acts. They were only saved because many of their girlfriends were present, and combined with some security footage were able to provide proof of innocence. They, similar to OP, had a highly incapacitated girl stumble up to their doorstep. None of them knew her, where she came from, or what she had consumed (alcohol, recreational drugs, hallucinogens, date rape drugs, etc.). They took her phone and started calling people until they got a friend, and prompted dropped her off with the RA of her dorm hall.
The saddest part is that as a result of having to prove their innocence, they had to admit that their girlfriends were drinking with them. Because some of the girlfriends were sorority girls, they ended up getting suspended for having an unregistered event while on social probation (they had a bonfire with the same girlfriends, and the fascists in Greek Life went after them for it).
As a result of this absolute mess, the IFC made an unofficial agreement for its members to turn away any girls who stumbled onto our properties. Now we just have to let them keep wandering on down the street, all because we're terrified of getting accused falsely of horrendous crimes (like UVA's fraternity did). If my friends' chapter didn't have their girlfriends over, they would have only had grainy security cameras that, at their angles, didn't provide much context to the situation. They could have ended up getting their names and reputations ruined.
I've seen two cases of guys getting roofied. Neither put anyone at risk. The first got honeypotted, we think, and ended up with his wallet emptied. The other realized something was off, and basically said "guys, I think I've been drugged. Take me home." Now, small sample set and all aside, this seems to (based solely on my personal experience) be problem that women are frankly awful at handling. Just one quick request for the ladies out there: Please, please, please keep yourself away from these situations. Don't take drinks from strangers (or frankly, anyone you don't completely trust), don't leave drinks unattended, and stick with a friend. This keeps you safe, it keeps you from accidentally accusing innocent good Samaritans from getting in some pretty serious trouble, and is basically better for everyone. Guys, do this: Document everything. Get it on video from multiple people when this happens, and don't stop filming. Call 911 immediately. Don't worry about her getting stuck with an underage drinking charge. Not your problem. It's not your job to help her home, and trying to do so only puts you at unnecessary risk. It sucks that there are horrible people out there, but us good folks have to suck it up and do our part to keep everything safe.
Tl;DR- This happens all the time. Fraternities have started to turn girls like this away if they stumble their way up, rather than help, because we could get accused of terrible stuff and people never doubt it. Girls, be smart. Guys, record EVERYTHING and let 911 handle it.