WELLINGTON (Reuters) - A search is under way in Antarctica for a missing plane with three Canadians on board, New Zealand rescue authorities said on Thursday. An emergency locator beacon from a Twin Otter plane flying from the South Pole to the Italian base in Terra Nova was activated late on Wednesday in the northern end of the Queen Alexandra Range. A search by a U.S. National Guard Hercules failed to spot the plane, and a second flight over the area was planned, the NZ Rescue Coordination Centre said. ...