The two things that this three countries have in common are that they are all predominantly Christian countries, and that all three of them have access to sea.
Mexico, Finland, and Ghana, are all predominantly Christian countries. They all fall into different branches of Christianity though, and the percentages vary, with Mexico having the highest, and Ghana the smallest percentage of the population practicing this religion.
All of the countries mentioned have access to sea. This has been and still is very important for their economic development because they are all able to dictate their own economies and their own trade with whoever they want.