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So implied status to apply for BOWP is not enough? Can you confirm?

You need to be holding a valid work permit to apply for a BOWP. Implied status i not enough.
 
My PR is under process (applied on Nov 18) and my PGWP will expire on July 5. When should I apply for the extension? CIC website mentions 4 months in advance...
How long does it takes for the extension approval? Is there any cost associated with it?
 
My PR is under process (applied on Nov 18) and my PGWP will expire on July 5. When should I apply for the extension? CIC website mentions 4 months in advance...
How long does it takes for the extension approval? Is there any cost associated with it?
Do you have AOR?