The spokesman said Peters will come to a decision sometime next week.
But he will be participating in Rugby World Cup promotional events before the big game.
These events will strengthen the "warm friendship and people to people links between Japan and New Zealand".
Sports Minister Grant Robertson has already announced he would be at the final – he's in Japan for a range of meetings in his capacity of Finance Minister at the time.
While in Japan, Peters will meet with Japanese Deputy Prime Minister Taro Aso, as well as other senior Government figures including the Ministers of Defence and Foreign Affairs.
Peters said discussions on the trip are expected to cover a range of issues, spanning New Zealand's bilateral relations Japan and well as the challenges facing the Pacific.
A range of regional security issues, including efforts in support of establishing peace and security on the Korean Peninsula, he also be talked about, Peters said.
Before heading to Japan, Peters will be in Korea where he will also be meeting with key Government officials.
While there, he will deliver a speech on New Zealand's relationship with Korea, as well as future opportunities for more partnership.
"The Republic of Korea and Japan are two of New Zealand's closest partners in the region with whom we share common values and interests.
"We have long-standing ties at the political, trade and economic levels," he said.