To report a fraudulent case, you should send the information to CSBA. I would also send a copy to CIC.
CIC's website with a list of the addresses is here: http://www.cic.gc.ca/english/information/offices/index.asp
I would send a letter to the Mississauga case processing centre, address above, and to the visa office abroad that is processing the file (if the person involved has not already arrived in Canada).
To report to CBSA, they have a toll-free telephone line:
Border Watch Toll-free Line 1‑888-502-9060
Here is the CBSA webpage with their contact information if you don't want to talk to them on the phone:
http://www.cbsa-asfc.gc.ca/contact/menu-eng.html
You do not have to give them your details. Appeal cases sometimes talk about how the visa office has received a 'poison pen' letter - which is usually anonymous. Nevertheless, the visa office will investigate it, and ask the applicant about the situation in the interview. So send them the information: they will take it seriously, though if they cannot verify the information themselves, nothing may happen. (Nothing may happen even if you do give them your name and contact information.)