Carnival Corp., which is working to revive profitability at its Seabourn luxury cruise line, said that next year it will shift a ship now sailing for Seabourn to the company's Holland America Line. The Seabourn Sun, at 38,000 tons the largest of the six Seabourn ships, will move to Holland America in April 2002 after the vessel finishes an around-the-world tour. Carnival, the world's biggest cruise group with 44 ships among its half a dozen lines, last month changed top managers at its jointly run Seabourn and Cunard lines.