"Opening the DHL NZ Lions Series against the best players from the Northern Hemisphere will no doubt be the biggest match of many of our players' lives - it will be a great occasion for them and the people of Whangarei."
Along with Randle and Maddock, McMillan will spend the next six weeks tracking players in the lead-up to a squad naming in April.
"We're aiming to play an entertaining brand of rugby which fits with the BaaBaas tradition of innovation and flair. For that we'll need a mix of new, young stars and more experienced provincial campaigners," McMillan said.
"It is a great opportunity for the match in Whangarei to set the scene for what promises to be an enthralling series with the British and Irish Lions.
President of New Zealand Barbarian Rugby Club, Ron Williams, says it was fitting that the Barbarians would open the series.
"The New Zealand Barbarian Rugby Club has a proud tradition dating back to 1937, representing every region over the years," he said.
"We're excited by Clayton, who has an excellent track record, coming on board to lead the Provincial Barbarians and looking forward to seeing the club's traditions passed on to the players who take on the Lions. We can't wait for June 3."