It's the first design competition in the corporation's 159-year history where the public will help make the final choice in the design.
Canada Post hopes to use the contest to raise awareness of mental health.
"We're asking entrants to convey important themes about mental health in a single image and make the winning stamp an ambassador for awareness," Mary Traversy, senior vice-president, Transaction Mail, at Canada Post, said in a release.
Canadians can submit designs online until Jan. 17. A short essay of up to 100 words should be included to explain why entrants think their design will raise awareness and understanding of mental health issues.
The winner will be announced in April.
As well as having their original artwork produced by a professional design firm and the resulting stamps issued for sale in September 2011, the winner will receive a framed enlargement of the stamp and a $500 honorarium will be donated to a mental health charity of their choice.
Canada Post made mental health its cause of choice in 2008, and a special stamp has been issued each year since then. Some $2.5 million has been raised for the foundation.
A surcharge on the mental-health stamp helps generate more funds for the foundation.
The foundation provides funding to community-based, non-profit groups helping people living with mental illness.