It seems to me that a major function of canon is to define
identity -- that is, to define certain books (or the views of
people who "own" those books) as essential and, as a set,
complete in some way or another.  The biblical canon also
establishes a powerful intertext, so that while folks might read,
eg, the gospel of Mark in a great many ways if there were no
canon (or if Mk were non-canonical), they are much less likely to
do so once it is securely contextualized by the canon.  It would
be hard for me to believe that canon and heresy/orthodoxy aren't
closely related --although there may be other reasons as well.
George Aichele