A canonization 1) does not invoke apostolic authority, 2) does not declare that it's a matter of faith to be believed by all, 3) does not specify the penalty for non-compliance.

3) We are to give religious submission to all the Pope's Magisterium and decisions on matters of faith and belief(except where it contradicts dogma but canonisations can't do that).

You have completely ignored the fact that theologians prior to V1 held different "levels" of infallibility, because they understood that there were different levels of "assent" required by different papal actions.  Post V1, we can no longer describe infallibility as having different "levels".  It either is, or it isn't.

So anyone quoting a theologian pre-V1 has to interpret their quotes accordingly.  Just as we would have to interpret St Thomas' thoughts on the immaculate conception as being deficient, in light of the Church's dogmatic statement.

There was never such a thing as a different level of infallibility. Infallibility means without error, mistake, etc. There's no such thing as partial or lesser infallibility, that's just called fallibility. The theological notes did not comment on "how" infallible something was, as there are no degrees of infallibility, but rather how much assent/submission a Catholic had to give. Every theologian has always believed canonisations to be infallible, all they've disagreed on is whether or not it's a mortal sin if a Catholic rejects that.

Belief in Papal Infallibility wasn't always de fide either, but does that mean Papal Infallibility only started to exist the moment Vatican I declared it?

The Immaculate Conception wasn't always de fide, but that doesn't mean it wasn't always true.

Just because someone doesn't believe something doesn't mean it's not true, even if they aren't punished for their lack of belief.

So, when last I tuned in this morning, here is what I attempted to say (before getting timed-out):

1) The premise of the OP is that canonizations as such are not magisterial teaching, and therefore cannot be the object of infallibility (and the consequent obligation for all the faithful to assent to them).

2) It was shown that Van Noort assigned to canonizations the lowest of theological notes, according to which, as Fr. Ott explained, free debate is certainly allowed.

3) Moreover, Pope Benedict XIV (creator of the modern canonization process which had been in place until the "revised" post-conciliar canonization process abrogated it), who, in his capacity of private doctor, opined that canonizations were infallible, acknowledged nevertheless (in the quote I provided by Fr. Hunwicke) that:

"plures magni nominis auctores [i.e., "Many great named authors"] deny that an act of canonisation is de fide."  

Cajetan would be foremost among them.

4) Cantarella, Loudismouth, and others supplied well known quotations from various catechisms and saints attesting in favor of infallibility, and I do not deny that for the last few hundred years, their opinion -as Van Noort acknowledges- is in the overwhelming majority (at least until recently).

5) Forced to explain how it could be that canonizations were infallible, yet theologians were allowed to publish works (receiving the Imprimater and Nihil Obstat) which contested that belief, the infallibilists had no answer.

6) I supplied it for them in the Fr. Hunwicke article just referenced (and found on p. 4 of this thread): The scope of infallibility was curtailed with the dogmatic definition at Vatican I, and consequently, some things previously thought to be infallible were shown not to be, as one of the conditions V1 required was that the object of infallibility be a matter of faith and morals.

7) But it is clear that the candidates for sainthood are not part of the divine revelation; they are not contained in the deposit of faith, either in scripture (unless we are speaking of biblical saints) or tradition, neither implicitly, nor explicitly.

8> As such, canonizations cannot be the object of infallibility, since the "faith" is precisely the totality scripture and tradition; nothing more, nothing less.

Consequently, it is ignorance which has led to a caustic anathema by the infallibilists, but in fact, they are wrong:

They have not understood the impact of Vatican I against the opinions of the saints, popes, and doctors whose positions, at lest on this precise matter, have been made obsolete by events transpiring after their own lifetimes (and fiercely debated within their own).

From the OP:

In other words, individual catholics get to "pick and choose" what saints they consider worthy of the title, and which ones they do not; relying solely upon their own whim, regardless of what the Holy See proposes.

I am free to reject Mother Teresa, for instance; but adhere to Padre Pio, just because I perceive "heroic virtue" in the later; but not the former. I am not talking about the act of veneration itself (which may be subjective); but just the internal assent that the person is in Heaven because the Church told me so.