Please read the following site.
http://www.ca.emb-japan.go.jp/canada_e/Visa/working_holiday.html
Prerequisites
Applicants for the Working Holiday visa must:
5. Possess a valid Canadian Passport and a return travel ticket
Applications
8. Return airline ticket or flight itinerary provided by an airline company or travel agency (Please note we are not responsible for tickets which are unusuable due to delay or denial or visa).