I thought Vatican I included the OUM as infallible and canonizations were part of the OUM? But maybe I am getting confused at this point.
Yes, the Vatican Council teaches papal infallibilty in
Pastor aeternus (session 4) as well as infallibilty of the ordinary and universal magisterium in
Dei filius (session 3).
The ordinary and universal magisterium is the magisterium of all the bishops all over the world, including their auxiliary bishops, and priests, and seminar professors etc., teaching, what has been taught "everywhere, always and by all" (apostolically authorized shepherds).
A canonization is not an act of the ordinary and universal magisterium, but an act of a pope. Thus, infallibilty of the ordinary and universal magisterium does not play a role. However, it is not needed to defend the infallibilty of canonizations, because the definition of papal infallibilty
ex cathedra does neither define nor imply fallibility of all other acts of the pope.