From the day you sign your application, in the past 4 years, if you were in a country or territory other than Canada for 183 days or more in a row (since the age of 18), you must provide a police certificate for each country or territory. If you cannot get a police certificate, there's a "Explanation" box on the application form. Exception: if you were in your country or territory of origin immediately prior to becoming a PR and landing in Canada and this time falls within this 4 year period, you are not required to provide a police certificate.
Source: CIT 0002 (01-2022) E