Which of the three largest nations in North America achieved its current political boundaries first?

Answer 1

Mexico was the first to finish its geo-political organizing in 1917. Canada didn't finish until 1999.

Answer 2

Mexico. It lost considerable land through the Treaty of Guadalupe Hidalgo which concluded the Mexican War of 1845.The United States only stretched from coast to coast before the War Between the States. Canada didn't enter confederation until after that war and it didn't add its last province of Newfoundland until 1949.