There is no "appeal" process to challenge a refusal of Canadian citizenship or a citizenship certificate. However, it's possible to start an application in the Federal Court seeking leave (permission) to commence a judicial review application, which is similar to an appeal. The principle difference is that the legal test is harder to succeed on for a judicial review. 

Seeking leave to the Federal Court and then proceeding with a judicial review is a highly technical procedure, which would be very difficult to pursue without the assistance of a lawyer.