Which of the following regions has a population exceeding 400 million?

The European Union (EU) is the correct choice because it encompasses a diverse group of member countries that collectively contribute to a population exceeding 400 million. As of recent estimates, the total population of the EU stands at approximately 450 million. This large population base is a result of the union of numerous countries, each contributing to the overall demographic figures.

In contrast, the United States has a population of around 330 million, Japan is home to about 125 million people, and Canada has a population of approximately 38 million. Each of these respective populations is significantly below the threshold of 400 million, which highlights the substantial demographic weight of the EU as a region in international affairs and economics.