I grant you that it is different, but you kind of left totally unaddressed the fact that it is not very powerful at the moment. The US is in far more danger than Canada.

Speaking as a Canadian: the general belief up here is that something like freedom of speech is not God-given, but is rather something we have built for ourselves using the mechanisms of civilization. I'm aware this is a long-term debate, philosophically, in America; but most folks I've talked to up here believe that rights are something we carve out of the world through our justice and policing systems, not something pre-existing that we're just recognizing.

Consider what freedom of speech means, in practice: to me, it means "you can say whatever you want, and you will retain all of your other rights, including the right to have police protection from those who would attack you for your words".

It doesn't mean "freedom from consequences" in some magical sense where people won't react to what you say or try to punch you in the face. It does mean you can engage the system to punish them for assault, though, and that you haven't given up those legal protections with your words.

I don't think it really means that you can't be fired / deplatformed over it, either. It's a relationship between you and the government, who agrees that they won't withdraw their other supports from you for your words. It also has exceptions: we've got hate speech laws here, though what most folks don't know is that you have to be posing a pretty credible threat, inciting groups to violence, etc (so you're actually still allowed to say a wide range of things that will anger others).

Now, we can imagine a stronger free speech protection - a second layer on top of the first - that says "you can say whatever you want, and your employer is forbidden from firing you over it" - but that kind of thing hasn't been created yet. I'd support it, personally, but I can see why it's a contentious concept.

So ... does that mean that under a thin veneer of democracy the USA are actually a theocracy like Iran, but christian-affiliated?

That would explain a lot of the recent actions by your current administration.

Yet it's the US that loses its democracy and freedom first, not all the other countries. I guess the distinction isn't powerful enough eh?

The belief of 'where' your rights come from has very little impact on reality - and in reality, it's the government (those that control the police, military) that grant you any rights whatsoever. The distinction between where your rights come from doesn't matter much when the people in power are willing to trample them either way.