To my knowledge, if JPII is canonized all it means is that he is infallible in Heaven, and that's it! The sedes can argue that the Church has erred....
You don't seem to understand the sedevacantist thesis. Sedevacantists do
not argue that the Church has erred for the acts of the Conciliar sect are
not acts of the Church.
It is not a matter of procedure, it is a matter of the infallibility of the Vicar of Christ and the Indefectibility of the Church.
And this is the crux of the issue, not just the issue of the canonizations, but the entire Conciliar anti-Church. In order to continue to believe that the Conciliar sect is the Catholic Church, one
is forced to abandon the doctrines of the indefectibility of the Church and the infallibility of the ordinary and universal magisterium. Moreover, one is forced to do so while denying that one is doing so and boil most acts of the Conciliar sect down to procedure and legalisms.
--The canonization process changed so canonizations are no longer infallible.
--The Novus Ordo wasn't properly promulgated so it is not really the official worship or, at least, isn't really mandatory.
--The Council of 1962-1965 didn't define any doctrine and is merely "pastoral", so nothing it actually teaches is really Church teaching.
Etc., etc., etc. Never mind that the Conciliar sect clearly behaves as if they have established a brand new Church with its own saints, its own doctrines, its own free-wheeling rites and that this new Church has
replaced the Catholic Church.
What an interesting time to live in, where Novus Ordites and Dogmatic Sedevacantists wait with anticipatory glee for one and the same event...
While I don't know about "Dogmatic Sedevacantists" because I don't really know any, I don't know any sedevacantists who "wait with anticipatory glee" for this canonization. We are hopeful, but not optimistic, that it will open they eyes of the faithful who are stuck in the muck and mire of Conciliarism.