Canada is in a group with Fiji, Portugal and Wales at the Gold Coast Sevens on Oct. 12-13.
Eleven players are unavailable for the event, according to Rugby Canada.
Tyler Ardron, Jeff Hassler and Phil Mack are with the Ospreys in Wales while Taylor Paris is playing for Agen in France.
Sean Duke (shoulder) and Jake Webster (leg) are injured. Chauncey O'Toole and Thyssen de Goode are unavailable due to personal commitments.
"Conor (Trainor), Mike (Scholz) and Adam (Kleeberger) are all recovering from knocks and we feel they're not quite game-ready," head coach Geraint John said in a statement. "However, we're hoping they will be available to return for the Americas Rugby Championship at some point in October."
"Having a large number of players unavailable for selection allows for a deeper roster and more opportunities for our younger players," he added.
Hirayama finished third in scoring last season on the circuit with 241 points behind Fiji's Joji Baleviani Raqamate (247) and England’s Dan Norton (264).
He also captained Canada at the Rugby World Cup Sevens in June.
Pat Parfrey and Pat Kay make their debut on the World Series circuit.
Connor Braid, James Bay AA, Victoria; Nanyak Dala, Castaway Wanderers, Saskatoon; Justin Douglas, Abbotsford RFC, Abbotsford, B.C.; Sean Ferguson, UBC Thunderbirds, Vancouver; Mike Fuailefau, Castaway Wanderers, Victoria; Lucas Hammond, Toronto Nomads, Toronto; Ciaran Hearn, Castaway Wanderers, Conception Bay South, N.L.; Nathan Hirayama (capt.), UVic Vikes, Vancouver; Harry Jones, Capilano RFC, North Vancouver; Pat Kay, UVic Vikes, Duncan, B.C.; John Moonlight, James Bay AA, Pickering, Ont.; Pat Parfrey, Swilers RFC, St. Johns, N.L.
Head Coach: Geraint John – Head Coach