The bill (which you can read here, it's super short: https://www.congress.gov/bill/117th-congress/senate-bill/623...) adjusts EST/CST/MST/PST etc to be +01:00. If you dig into the bill it's referencing, it defines US timezones based on UTC so this is just adjusting the time +1 hour based on that original bill.

Oh that will be a massive mess. So now the poor sod writing libraries have to take in account the offset changing in 2023...

At least in BC we already have legislation to do this as soon as the western states do.

In Alberta it just got voted down by a very slim margin, so if the US made the switch I expect that would be enough to swing it there as well. I expect other provinces would follow suit as well, assuming the federal government didn't just make the decision for everyone (which they probably would if the whole US went to permanent DST).

Question from a dumb American: Does Canada have a lot of laws that only go into effect if the US or nearby US states do the same? I've never heard of that before.

I can't recall any others (edit: aside from obvious things like laws relating to trade agreements or defense cooperation), but this one makes some sense to keep the time zones consistent. Also since I made that last comment I learned that Ontario has a similar plan w.r.t. NY. So it definitely appears Canada will switch when the US does.

In California the law of the land is already that we'll switch to permanent DST when the federal government allows it.

Ontario has already passed a bill saying that it will make DST permanent if 1) Quebec and 2) New York State make it permanent

The text of the bill shows the latter: EST/CST/MST/PST/HST/AKST shift by 1 hour.