A lot of Canada doesn’t have what you would call “infrastructure” until you’re well within range of the US Border. They’re also about equally insulated from foreign invasion and I think any US invasion that called for invading Canada first would be facing challenges that make invading Russia in the winter look like a pleasant stroll in the park.

Mexico is also about equally protected from foreign invasion. I guess their biggest threat would be us, and not without precedent, but they are not a threat to us. And just as Mexico is not a threat, neither are the nations south of Mexico a threat to Mexico. This was all true even in Lincoln’s time.

So, yeah, suicide it is. That includes any kind of internal fracturing.