There's no minimum income requirement to sponsor your wife.
Technically your wife could move to Canada with her PR status without you, but this is not what the family class PR visa is intended for and that's why you need to show you (the sponsor) plan to move back to Canada too. There are examples given in the application package for what sort of proof you can give and you can include an explanation letter in which you'd outline your plans to return. Once your application is being processed you could be asked to provide further proof.