Your PR visa is usually valid for a year from the date of your medicals. If you see that you will not be able to move completely before it expires, you can come to Canada to land as a PR and then leave again. You can give your brothers address for your PR card but do not tell the immigration officer that you will not be there when it arrives or they may decide to withhold it until you are back to stay.
Your brother can mail you the PR card when it arrives. If this doesn't work out, if you are visa exempt, you can come back to Canada using your landing documents and if you are not visa exempt, you can get a PR travel document to go back.
Hi Leon
Thank you very much for your response.

It's very good that the visa period is one year.
I will remember the point about not telling my story to the officer.
No I'm not visa exempt, I'm Iranian and now living in Europe (don't have any European passport)
But if I still couldn't make it in 1 year, how can I apply and receive a PR travel document while I'm outside Canada?
I was checking a page about this , maybe I'm wrong... but don't they only issue the PR travel document to people residing inside Canada or people who have already received their PR Card?
and , do you think my brother can mail the PR Card to me? maybe there are some restrictions on type of documents possible to mail.
You know I still think it's a little risky. we never know when a rule changes.
well... I was thinking , I may get married before migration
is it possible that my wife enter Canada by herself?
and also maybe we come together and do all initial regulations, then I leave and she stays to receive the PR cards
I hope it all work out well
thanks again