Not counter attacking would be an agreement that the attacker can settle to their benefit any conflict by sending a nuke, without equal consequences for them, and so encourage them to sending more nuke.
The only use of nuclear nuke is to replicate if someone else use theirs (or rather to let them know you would, so they don't). If you don't replicate, you might as well dismantle all your nukes after that.
Unfortunately, there is no other way, if someone use a nuke, we must all die. I think Poutine and the others are well aware of that. Well I certainly hope so.
Haha well, in case you didn't know, it turns out it's also what the madman who is attacking Ukraine now is named in French - and I assume in French Canadian too ? So I hope our friend from Quebec will not mind too much ^^
Reasonable people can be hard to come by when the world is ending. I imagine that even the most ordinarily level headed person might become a bit emotional when nukes starting dropping on their country.
Also 'winner' might not be the best choice of words for this situation.
So the first one would be the winner.