A literary canon is a group of literary works that are generally accepted as representing a certain field. For example, one could talk about the canon of Elizabethan drama, which would include the works of William Shakespeare. The term "canon" can be applied to many different groups of work.
A fictional canon is a subset of a literary canon. Fictional canon is defined as works accepted as part of the story in an individual fictional universe. Fictional canon can be applied to any series of fictional stories or novels. For example, J.K. Rowling's "Harry Potter" books make up the canon of that fictional world.