As part of applying for Permanent Residence in Canada, the applicant must undergo an FBI background check to obtain a police certificate: http://www.cic.gc.ca/english/information/security/police-cert/north-america/united-states.asp
How long will this certificate be valid? I can't find any information about the lifespan of this document. I'm looking into applying for PR status soon and I'd like to get a head start on this process, but I don't want the certificate to expire before my PR application finishes processing.
For countries where you have lived for six months or more, the police certificate must be issued after the last time you lived in that country.
andFor the country you currently live in, the police certificate must be issued no more than six months before you apply.
Not sure how much that helps you.