Orr, who is not on the Nationals' 40-man roster, played in the 2006 Classic and went 1-for-12 for Team Canada. For Rivera, who is one of the Nationals' top relievers, this is the first time he will participate in the Classic.
Washington could have had more players in the Classic, but outfielder Roger Bernadina and pitchers Shairon Martis and Daniel Cabrera dropped out.
Bernadina and Martis, both from the Netherlands, felt it was more important to stay in Spring Training camp in an effort to make the 25-man roster than to play in the Classic. Cabrera, who is from the Dominican Republic, is playing in the National League for the first time, and the pitcher wants to get better at bunting and swinging the bat.
The Classic's first round opens March 5 in Tokyo, with defending champion Japan facing China. Mexico City, Toronto and San Juan, Puerto Rico, host the other three first-round brackets, as follows:
Tokyo (March 5-9): Japan, China, Chinese Taipei and Korea
Toronto (March 7-11): USA, Canada, Venezuela and Italy
San Juan (March 7-11): Puerto Rico, Dominican Republic, Netherlands, Panama
Mexico City (March 8-12): Mexico, Cuba, South Africa, Australia
It's a double-elimination format in the first two rounds. The winners from Toronto will meet the winners from Puerto Rico in the second round at Miami's Dolphin Stadium, while the winners from Tokyo will meet the winners from Mexico City in San Diego's PETCO Park.
The semifinals and finals are on March 21 and 23 at Dodger Stadium.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.