Boyd and Leilua join Cowboys co-captains Johnathan Thurston and Matt Scott, as well as Michael Morgan and Justin O'Neill, in the train-on squad.
Kangaroos Coach Mal Meninga said he was pleased with the potential for the Four Nations squad based on the Prime Minister's XIII's 58-0 victory over the Papua New Guinea Prime Minister's XIII in Port Moresby last Saturday.
"The squad is taking shape very well," Meninga said.
"I was really pleased with the performance of a number of players in Port Moresby and it enhanced my thoughts on a number of players.