Watanabe, 28, averaged 5.6 points on 49 percent shooting, including 44 percent on 3-pointers in 58 games with the Nets last season.
Metu averaged 4.9 points and 3.0 rebounds in 66 games. He spent each of his first five seasons with the Kings.
Along with the Nets, he has spent time with the Grizzlies and Raptors since going undrafted out of George Washington in 2018.
Both Yatanabe and Metu reportedly received one-year contracts and are expected to serve as frontcourt reserves in the Suns’ start-studded starting lineup of Kevin Durant, Devin Booker and Bradley Beal.