Classic case is health care (‘look, we spend less than the US and have free healthcare’) where instead of looking up to countries with better healthcare outcomes than us, we look down on America and act smug. Other cases include our climate record, and post secondary education.
Who is saying this, other than low-information Americans on social media hung up on the word 'free'? Every Canadian knows that the reality is much more complicated with capacity shortages since Covid, and an opportunistic provincial government in Ontario doing its very best to push further privatization.
Anecdotally it's usually used when someone starts to criticize our healthcare system.
Since US and Canada are so similar, a lot of the discussion of identity are around the differences, which to me is a weird way to talk about a national identity.
It also comes up a lot when someone mentions something positive about the US that Canada struggles with, say economic growth - then it becomes a common refrain of “yes, but at least X is better in Canada than the US”.
It’s also used commonly in discussions in healthcare - any change is described as “Amerification” of the healthcare system even those the change would just make Canada more like European systems.
Maybe it’s unavoidable being right next door to the US, I don't know.
Also, why the hostility? I've never met a Canadian that expressed a sense superiority about not being part of the USA. I've met plenty who are proud of their national identity, and there's nothing wrong with that. It's quite admirable too, in my opinion. Nation-building isn't easy.