Final answer:
France is the country that has Le Havre, a significant port at the mouth of the Seine on the English Channel, and it is the second busiest port in the country.
Step-by-step explanation:
The country that has Le Havre, at the mouth of the Seine on the English Channel, and the 2nd busiest port in it is France. Le Havre is a significant maritime port involved in global economics and serves as a major gateway for trade entering and leaving France. Given its strategic location, it is essential to the movement of goods along international trade routes, much like other major ports such as Rotterdam in the Netherlands, which is noted as Europe's busiest port.