“to difference in their Biblical canon.”
There are no canonical differences. I suggest using actual Orthodox sources and not protestants talking about the Orthodox.
As for Ineffabilus Deus - it’s the formulation of the doctrine which has been taught long ago.
“All these things our illustrious predecessor, Alexander VII, summed up in these words: “We have in mind the fact that the Holy Roman Church solemnly celebrated the Feast of the Conception of the undefiled and ever-Virgin Mary, and has long ago appointed for this a special and proper Office according to the pious, devout, and laudable instruction which was given by our predecessor, Sixtus IV.”
This was written in the early 15th century - so the Doctrine was quite old then.
http://www.papalencyclicals.net/Pius09/p9ineff.htm
Strictly speaking, "canonical" indicates an indisputable canon on the part of the Orthodox, which is not the case, however, to assert there is no consistent difference btwn the books Orthodox hold as part of their Bible versus Rome requires you to read Orthodox sources.
What is the Old Testament canon of the Orthodox Church? Is the Apocrypha recognized as canonical?
ANSWER:
The Orthodox Old Testament includes both canonical (or protocanonical) books and supplemental books which are not considered canonical (i.e. protocanonical) but deuterocanonical or in Greek Anaginoskomena ("to be read").
Deuterocanonical is used here in a sense that is different than the Roman Catholic sense. In Roman Catholic terminology, "deuterocanonical" means approved later but with the same canonical authority. In the Orthodox use, "deuterocanonical" means having secondary authority, but useful and part of the Biblical library (no Orthodox Bible would not contain them). The Scriptures testify to Jesus Christ and since neither Protestants nor Jews recognize these Scriptures, their power to serve as witness is inferior. However, they are read in the Orthodox churches and have great value. This view is faithful to the position of the earliest Christians (i.e. Justin, Origen) as well as the distinction connected with Athanasius and other important Fathers. - http://www.orthodoxanswers.org/answer/39/
In an Orthodox Bible there are 49 books in the Old Testament canon. Roman Catholics only accept seven so called Deuterocanonical books, so their Old Testament has a total of 46 books (sometimes counted as 47). - http://orthodoxwiki.org/Apocrypha
The Roman Catholic and Greek Orthodox lists of accepted Deuterocanonical books differ (the Greek list is longer). There are even slight differences between the Russian Orthodox and Greek Orthodox versions of the Old Testament. - http://www.orthodoxstudybible.com/articles/who_decides/
In terms of "canon," the Orthodox Old Testament includes the 39 universally received ("canonical") books as well as the books found in the Septuagint which have always been read, used or explicitely quoted by the early Christians (Letter to the Hebrews, St. Polycarp of Smyrna. These books are part of the Orthodox Bible and lectionary but not with full canonical status; they are often called "deuterocanonical" or "to be read" (Anagignoskomena (αναγιγνωσκόμενα)). As a result, it can be said that the canon of the Old Testament is somewhat "open" with degrees of witnessing authority. http://www.orthodoxanswers.org/orthodoxbibles
...most Orthodox scholars at the present day, however, following the opinion of Athanasius and Jerome, consider that the Deutero-Canonical Books, although part of the Bible, stand on a lower footing than the rest of the Old Testament." - Bishop Kallistos (Ware), The Orthodox Church, (Penguin Books, 1997), p. 200 - http://www.orthodoxchristianity.net/forum/index.php?topic=8311.0;wap2
It is also to be noted in addition that the Orthodox Anagignoskomena do not exactly coincide with the Deuterocanonical books (only seven) of the Catholic Bible....Not to mention, of course, that with the so-called Oriental Orthodox Church the problem of the canon is still more complex even for the N.T., ranging from a shorter canon to a much wider one (37 books in the Ethiopian Church) - (AN ORTHODOX HERMENEUTICAL PERSPECTIVE) http://users.auth.gr/~pv/inspiration.htm