The North American duo will be permanent additions to the IRB-funded annual tournament which features Japan, Tonga, Fiji and Samoa.
"This exciting enhancement to the IRB Pacific Nations Cup is good news for Japan, Canada, USA and the Pacific Islands," IRB Chairman Bernard Lapasset said.
"We now have in place an annual high-calibre competition that will deliver compelling matches, while also fulfilling the high performance needs of our Unions."
Japan, World Cup hosts in 2019, will stage the final round in June, though holders Samoa will be absent as they take a sabbatical to compete in a four-team series in South Africa against the Springboks, Scotland and Italy having qualified as the best tier two side.
The initiative is the latest move by the IRB to try to improve standards in world rugby, which is dominated by New Zealand and a handful of other nations.
"The IRB has a long-term commitment through our strategic plan to create greater levels of quality test competition for tier two nations in order to boost the competitiveness of the world game and rugby World Cup," IRB Head of Development and Performance Mark Egan said.
"To that end we are investing more than 10 million pounds ($15.87 million) per annum in tournaments and high performance programmes for our targeted group of Strategic Initiative Unions."
While undoubtedly talented, the Pacific Islanders have suffered from a player drain to bigger nations, with Samoan-born Manu Tuilagi currently playing centre for England and Fijian-born Radike Samo representing Australia in the backrow.
Despite the player losses, Samoa have moved up to seventh in the world rankings after wins away to Wales and Australia in the last 18 months, while Tonga won 21-15 in Scotland in November, their first victory over the Six Nations side.
With the expanded Pacific Nations Cup (PNC), coaches of the tier two teams are hopeful the upsets will continue.
"The new look PNC will provide the Eagles with consistent fixtures against some very competitive teams, this can only be good news for the Eagles as we plan our path to Rugby World Cup 2015 in England," USA Rugby Chief Executive Nigel Melville said.
Japan head coach Eddie Jones, who took Australia to the 2003 World Cup final, agreed with the Englishman.
"The IRB Pacific Nations Cup is a wonderful opportunity for Japan and all participating unions to elevate their performances to a higher level in order that we can be more competitive at future rugby World Cups," Jones said.
- Sports & Recreation