NEW YORK -- A watercolor by Vincent van Gogh that was seized by the Nazis during World War II will be sold next month at auction in New York, where it is expected to fetch a price of $20 million or more, the auction house Christie's announced.Christie's is auctioning the 1888 work, “Wheatstacks,” after facilitating negotiations between the Texas oilman's heirs who own it now and the heirs of two Jewish art collectors who owned it at different times before it was looted by the Nazis.