Here some Hetalia pairings that make NO sense at all.
France x England - How does this even work? They hate each other's guts. I mean, so wars between them make this 'canon'? NO. The wars just prove that they hated each other. A LOT. They would never have sex or kiss or anything. They would kill each other 9,000,000 times before that happened.
Spain x England - Again, how does that work? They also hate each other's guts. And people say "OMG ITS SO CANON!" How? England and Spain hate each other, and that's why England sunk Spain's armada, and now Spain hates him even more. Again, they would kill each other 9,000,000 times before they kissed or had sex.
Russia x America - This one is the stupidest one ever. The Cold War did NOT make this canon. All it did was prove that they hated each other. I'm Russian and I personally despise seeing my country making out with the same country we hated. This pairing, just no, no.