If I were you, I would put all the dates of the visa refusal. Also, give reasons why the other visas were rejected. If you are honest with immigration officers, you have a good chance of being issued a canadian PR visa. Don't hide anything from them at all. Even your own conscience will be clear if you hide nothing from them. Your failed assylum or refused USA and New zealand visas have nothing to do with your canadian PR if they are not rejected based on criminal reasons so go ahead and be honest with your application. Good luck to you.
I share the above views in it's entirety. Good piece of advise. I'll do the same, if I were in those shoes.