http://www.ppt.gc.ca/support/faq.aspx?lang=eng&id=2101
You do not need to return your passport if it has expired. However, if you are applying for the Simplified Passport Renewal Process you must enclose any Canadian passport issued to you within the last 6 years.
Do I need to include my valid passport?
Yes; you must submit your valid passport with your application for a new one. Note that a previous Canadian passport will be accepted as supporting identification provided that all of the following conditions are met:
http://www.ppt.gc.ca/support/faq.aspx?lang=eng&id=2102
The passport is still valid or has expired within the past year;
The passport is submitted with the application. Photocopies will not be accepted; and
The name indicated on the passport and the application are the same.