It really depends on what commonalities are you basing your question from. For example:
Both countries are federal republics, so countries similar to them would be Austria, India, Nigeria, Russia or Nepal.
Both countries are on the Americas, so Argentina, Brazil and Chile would also be on the same group.
Both countries have a large Hispanic population, so again, Argentina, Brazil and Chile would be similar to them.
The main countries that border the US are Canada, and Mexico.
When the US invaded Mexico in 1914? Yes; those where the ABC countries (Argentina, Chile, Brazil) to prevent a new US-Mexico war.
Canada and Mexico.
Mexico and Canada.
Mexico
The two countries that border the US is Canda (to the north of the US), and Mexico (to the south of the US).
The US, Mexico and perhaps Cuba.
Canada, Mexico
Mexico and Canada
Canada and Mexico
Mexico, Canada,
Mexico and Canada