Generally IRCC requires PCCs to be submitted along with the PR application (e-APR). In some cases, they require a consent from applicants instead of the PCC and IRCC itself collects the respective PCC from concerned authorities (e.g: New Zealand). Also, in some cases if requested, they would give additional time to submit PCC after the e-APR (e.g USA PCC by FBI that takes long time to complete).
Check out below link for country specific process to collect and submit PCCs. If in doubt, feel free to ask in forum again.
http://www.cic.gc.ca/english/infORmation/security/police-cert/index.asp