I lived in Japan for 11 months and now I am in Canada and applying for PR under express entry with CEC, so when I should start process for Japan PCC, is it something I need to wait for the letter from IRCC to initiate Japan PCC?
Police clearance of all the places you lived for more than 6 months should be submitted. You dont need it before ITA but when you are responding to ITA you should submit it.