Massachusetts Republicans will choose candidates to challenge U.S. Sen. Elizabeth Warren and U.S. Rep. Stephen Lynch in state primaries. The contests Tuesday top the list of federal, state and local races that will be held across the commonwealth. Warren is seeking a third term and is unopposed for the Democratic nomination. The possible Republican nominees are industrial engineer Bob Antonellis, Quincy City Council President Ian Cain and attorney John Deaton. Deaton is by far the best-funded candidate in the GOP field, thanks mostly to the $1 million he loaned to his campaign.