Poll question and OP question aren't exactly the same.
What would cost HF to crash the fastest/for longest? It's definitely one of the top 2 choices. Every hockey fan would be watching because it's the finals, and the reaction/drama with those matchups (or leafs winning) would definitely cause HF to crash.
But if you're asking about biggest meltdown, as in people going "omg! I can't believe this!" and people being genuinely upset, that's a different answer. But it wouldn't necessarily cause the servers to crash since not everyone would be getting/reacting to the news at the same time. So for meltdowns, I would probably rank in order:
1. Cup Winning team cheating. Depends on what the cheating is though - i'm not sure how you can cheat at hockey, it would have to be something super significant, so not a goalie pad being too big for example - more like bribing a referee or such. But if so - 100% this one, fans would be livid
2. Edmonton/Pittsburgh winning 1st overall of a generational prospect draft (so a Crosby/McDavid caliber prospect or better).
3. McDavid requesting a trade
4. Leafs win cup
5. The all Canadian finals
6. Refs fix a game (I assume this is a rogue ref acting on his own - if this was mandated by the league, it would be higher).