http://www.cic.gc.ca/english/helpcentre/answer.asp?q=048&t=5
I’ve lost my citizenship card/certificate. How do I replace it?
To replace your citizenship certificate, follow the steps to
apply for proof of citizenship. You must use this process if your certificate was lost, stolen, damaged or destroyed.
If your card/certificate was lost or stolen, you should report it to your local police department. You do not need to tell CIC it was lost or stolen.
We stopped issuing the plastic wallet sized citizenship cards with the commemorative certificates in February 2012. If you lost your card or need to make a change to it, you must
apply for a citizenship certificate.
We will not send you a new card.
The commemorative certificates that were given out with the plastic citizenship cards
cannot be used as proof of citizenship. We will not replace a commemorative certificate.
If you are not sure if you have a commemorative certificate or not, see the
examples of citizenship certificates. If your certificate does not look like these examples, you have a commemorative certificate.