You’re raising really valid points Tim — the “advertised event” language is pretty open to interpretation, and I don’t think most pilots (or police, for that matter) have a consistent definition yet. Your examples — regattas, street parties, Facebook-organized events — are exactly the grey areas that are going to cause confusion.
Back when I was flying helicopters under the old Air Regulations, we dealt with similar wording around “open air assemblies of persons.” It was vague then too. But the rule of thumb we followed was always to err on the side of caution. If there was any chance it could be interpreted as an organized gathering, we treated it that way. Nobody ever got in trouble for being too safe.
I suspect Transport Canada and law enforcement are going to focus mainly on the high-profile stuff — stadiums, parades, festivals, protests — especially where there’s media or security involved. But until they define “advertised event” in plain language, it’s going to feel murky. For now, I’m treating it like I did in my helicopter days: if people were intentionally gathered for something, and someone promoted it in any way, I assume it qualifies.