World Rugby said in a press release that it was "creating an annual competition and rivalries like those seen in the men’s Six Nations and Rugby Championship".
It said the finals in the revamped annual competition will alternate between Japan and the United States.
The cup will start with two three-team groups in August with Fiji, Samoa and Tonga in one and Japan, the United States and Canada in the other.
Each will play one home game and one away game as they face the other two teams in their group once each.
All six countries will then head to Japan in September for the finals, which will open with the two third-place group finishers facing off and the two semi-finals.
The following weekend the two semi-final losers will play for third and the winners will meet in the final.
The three games on the first weekend will be in Tokyo. The two on the second weekend will be in Osaka.
Japan coach Eddie Jones told World Rugby that he was looking forward to the competition.
"The Pacific Nations Cup is really important for Japan because it allows us to play regular tests against strong countries in tournament conditions, which is great practice for the players for the Rugby World Cup," said the former Australia and England coach.
"The Pacific Nations Cup fits in right next to the Rugby Championship and Six Nations in providing that regular competition for Pacific nations."
Tonga Rugby Union Acting CEO Aisea Aholelei said: "Tonga will take this challenge with a smile and a thumping heart."
The Pacific Nations Cup has gone through numerous configurations since it was first contested in 2006.
Fiji and Tonga are the only sides to have featured in every edition, Samoa having missed 2013.
Canada and the USA have both taken part in four previous tournaments, most recently in 2019, while Australia A, New Zealand Maori and Junior All Blacks have also participated.
Non-Pacific nation Georgia were invited once, finishing third in 2018.