When talking about nation states and multinational states the nation part refers to a unified culture and the state us the political organization. So a nation state is a country that is defined by its culture and (generally but not exclusively) contains most if not all of the members of that culture within its borders. A multinational state is one that contains multiple cultural nations.
So Finland, for example, is a nation state because it is defined by its Finnish-ness. Whereas Belgium is a multinational state because it contains multiple cultures.
I'm not the best at explaining that distinction, but hopefully that should be sufficient for you to look up more details on your own.
As for Canada, Quebec is pretty clearly a culturally distinct nation from, say, Ontario. But saying that it is a cultural nation does not suggest it has any distinct political differences from Ontario.
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