ok, seems I got the answer from CIC. It seems we do not need Canada police clearance
thanks
Police certificates
You and your family members, who are 18 years of age and older and are not permanent residents or Canadian citizens, must provide a:
valid police certificate, or
police clearance, or
record of no information.
Provide these documents for each country other than Canada in which you and your family members have lived for more than six (6) months consecutively during the past ten (10) years. If you or your family members were under 18 years of age when you lived there, you do not need to provide a police certificate.
The certificate must have been issued no more than three months prior to submitting your application. If the original certificate is not in English or French, then you will need to submit both the certificate and the original copy of the translation prepared by an accredited translator.
We will also do our own background checks to determine if there are grounds under which you and your dependants may be inadmissible to Canada.
Please consult our website for specific and up-to-date information on how to obtain police certificates from any country.