Just like how China doesn’t pay the tariff, it’s US importers who do, in this case Facebook doesn’t pay the tariff, it’s Canadian advertisers that would, on top of whatever Facebook is asking for. It would only hurt Facebook if you applied a fine or tax directly to their Canadian profits or prevented them from doing business in Canada, and even then... with other countries, the sway is, “you’re a citizen of our country, you have to follow the law, it’s easier that way” but if you’re not actually a citizen, have legal defense and possible substitutions in place, and ultimately, the only penalty is likely a slap on the wrist and a request you somehow further can’t ignore, well... it comes back to other countries on their own don’t have sway if the US or host nation doesn’t make the same request and you don’t have immediate travel plans to that country (and, of course, the country follows rule of law and/or you’re protected by your host country’s legal system...) That said, anyone in the country making such a request that works for an affected company would have to follow the laws of that host country over company dictates, or face legal consequences...