Help me decide on a medical alert device -- pendant or watch?

I have not researched this field. But if you already have an android phone, and Android-compatible watch may be the way to go.

This looks like a decent review of the field

That’s a very informative survey of current smart watches, thank you. But since I have to get a new phone anyway, and don’t use it for anything sophisticated, I’m happy to get the small and sturdy iPhone Air and the Apple watch SE3. I hate Apple’s closed “walled garden” approach, but for me it’s just a phone and just a personal security device.

Indeed, this is it. In the US I switched fron Verizon after 25 years because it was godawful expensive even with limited data. I went with Visible, which uses Verizon towers but is only $25USD a month unlimited everything. Nary a problem.
And yes, I agree, change is extra hard and stressful when so much else is changing too.

I think phone service has more limited choices and is mostly more expensive in Canada than in the US.

This is correct. Cellular services in Canada are basically an oligopoly consisting, in my opinion, of a conspiracy of a small number of major carriers who successfully prevail against government price regulation. Canada has been a leader in communications technology because of its size and historically sparse population, but, sadly, not a leader in price competitiveness.