After the French and Indian War, the land boundaries changed because France was completely ejected from continental North America. Where France had once owned a great deal of land on the continent, it now owned none.
Specifically, France gave its Canadian territories to Britain after the war. It gave the Louisiana Territory (what was later acquired by the US as the Louisiana Purchase) to Spain. Spain gave Florida to Britain.
So, after the war, the British owned all of North America east of the Mississippi River and Spain owned the Louisiana Territory. France no longer owned anything on the continent.