Citizenship & Immigration Canada requires most foreign nationals applying for termporary or permanent residence to obtain police clearances to verify that they are not inadmissible to Canada.
You must obtain a police clearance for any country in which you have lived, for a period of six (6) months or more since the age of 18. If you were living in the United States of America, you will most likely be required to obtain a police clearance from local State Police along with an FBI certificate.