Mexico. No doubt.
Mexico, although plagued by corruption and cartels like many south american nations, Has a strong Military, with a decent economy. Mexico’s current GDP is 1.28 Trillion dollars, to Cuba’s 77 Billion. Combined with their economic crash around 2014, Cuba could not afford a war.
Also, imagine Cuba like an island version of North Korea.
At the end of the day, both North Korea and Cuba are hopelessly out of date in the field of military technology. Meanwhile, Mexico, supplied by the united states, will easily crush Cuba’s resistance, with superior technology and funding.
Also, they are terrifying.