Final answer:
Mexico is the country most likely to have a large population of Christians today due to its historical patterns of Christian diffusion.
Step-by-step explanation:
Considering the historical patterns of Christian diffusion, the country most likely to have a large population of Christians today is Mexico. Mexico has a long history of Christianity dating back to the Spanish colonization in the 16th century. The majority of Mexicans today identify as Christians, with the Roman Catholic Church being the dominant religious institution.
Learn more about Christian diffusion and population in Mexico