Based on the provided data on the population of the United States by region from 2000 to 2014, we see that the populations in each region are increasing. The overall population rose from 275 million in 2000 to 325 million in 2014, indicating a growth trend.
While the question asks about the future trends of both the world’s population and the U.S. population, it's useful to note that global population trends generally show an upward trajectory, though the rate of growth may vary by region.
Considering these observations, the most reasonable conclusion is that:
Both will continue to grow at a steady rate.
This option aligns with the indications of population growth observed in the U.S. data and the trend of increasing global population.