Even California's labor laws are not going to be close to anything in Canada. And I don't know how many Twitter folks are remote, but if they're not in a very small minority of states, they're basically at the whims of management.
At the end of the day, Twitter is under new management and it is within management's right to change to circumstances of your employment. If they start pushing night and weekend work, and you don't deliver, that alone isn't necessarily a violation of any law. You didn't perform, and it's completely possible that your termination is legally for cause, even in California.
Employment law is very complex and honestly the situation will vary drastically even among similarly leveled folks on the same team fired at the same time. What kind of notification you're given, what kind of documentation there, previous reviews, etc. all play a role.
I think it's shitty to try to squeeze out people like this but just because it's shitty doesn't mean it's illegal or that it's a good idea to sue over it.