Unless both peoples buy wholeheartedly into nations without borders, this ain't happening. Unfortunately this could only happen sustainably if it happens on the basis of the working classes realizing their commonality and closeness. If it happens on the basis of free trade, the capitalist class will exploit the arbitrage opportunities between the two countries' working classes while turning those classes against each other, so they don't notice they're being co-exploited.
Unless both peoples buy wholeheartedly into nations without borders, this ain't happening. Unfortunately this could only happen sustainably if it happens on the basis of the working classes realizing their commonality and closeness. If it happens on the basis of free trade, the capitalist class will exploit the arbitrage opportunities between the two countries' working classes while turning those classes against each other, so they don't notice they're being co-exploited.