I’ve heard people say that the underlying physical infrastructure is older, but I think that’s a bit of speculation, although reasonable. The current outage is attributed to a “thermal event”, which does indeed suggest underlying physical hardware.
It’s also the most complex region for AWS themselves, as it’s the “control pad” for many of their global services.
If your customers are clusterrd in Toronto and Montreal, it probably makes a lot of sense to use ca-central-1. If you've got a lot of customers in Western Canada, us-west-2 is gonna have better network latency.
Other than a couple regions that had problems with their local network infrastructure (sa-east-1 was like that), there's little or nothing to differentiate the regions in terms of physical infrastructure and architecture.