What makes you say "certainly," especially in the hypothetical scenario where the US is unstable? Canada has a relatively much shorter history as an independent nation. Canada heavily benefits from its southern neighbor, and has a host of domestic economic issues (low wages, high housing prices; whatever the farmers are on about) that could cause instability as well. I think Canada is reasonably stable, I just quibble with "certainly" and "more" politically stable as compared with the US.
Canada will not invade allies and will adhere to the rule of law. Their forward looking economics are more favorable as they strengthen ties with China and Europe. By decoupling from the US, their economic risk declines, and their sovereign debt risk is downstream of that.
>>especially in the hypothetical scenario where the US is unstable?
How does it feel to bury your head in the sand so hard that you can't see what's happening around you?
Your "long history as a nation" mostly means you have a flawed constitution, no counter powers, a broken political system and absolutely _zero_ attempts to fix it.
There's a reason proper countries have had 5+ constitutions and keep changing them.