Help Sponsoring Niece

This is a complicated one....

I've sponsored my wife from Guyana and she is now processing to be a Canadian Citizen. We have been trying to get our niece over here to stay with us permanently but we have had no luck in the matter. Yesterday our nieces father who has not been a part of the child's life since birth contacted our family in Guyana to say he has been granted permanent visa status in New York and is being allowed to take our niece if we would allow it. We are trying to figure out that if her mother signs a document releasing her rights to the father and if he takes her. Is there a way we can sponsor her to come up to Canada to permanently stay with us?

What would be the process and where do we being? We are giving the final decision of staying with her father or coming with us to her but we need to know how to bring her here if needed.

Thanks,