Dwane Casey of the Toronto Raptors has been selected as the National Basketball Coaches Association’s Coach of the Year for the 2017-18 season, according to two people with knowledge of the voting. Casey will be formally announced as the winner of the N.B.C.A. trophy — which is named in honor of the association’s longtime executive director Michael H. Goldberg — later Wednesday according to the people, who were not authorized to speak publicly about the results.