The Collaborative International Dictionary of English v.0.48:

Canonicity \Can`on*ic"i*ty\, n. [Cf. F. canonicit['e].]
   The state or quality of being canonical; agreement with the
   canon.
   [1913 Webster]

The Free On-line Dictionary of Computing (30 December 2018):

canonicity

    The extent to which something is canonical.

   (1995-03-03)