Not everyone would conclude with the critics that "canonization" took/takes place by fiat from religious authority.
I would not say that the content of the OT was "canonized" in stages that correspond to the divisions of the Tanach, i.e. first the Law is recognized, then the early and latter Prophets, then lastly the Writings (but not before the Christian era began already). This view grows out of a rejection of Mosaic authorship of the Pentateuch, the rejection of predictive prophecy, and the view that Israelite religion is absolutely NOT unique, but is just another species of (ANE) religious expression.
Why is Daniel subsumed in a category outside the latter Prophets? This is difficult to determine, nor can we say for certain whether he once WAS listed in that division, and could have been moved/removed, or why. It could have something to do with his being outside the land, a servant of foreign kings, and an exilic prophet (but so is Ezekiel). Perhaps it has to do with the fact that almost uniquely it contains lengthy portion in Aramaic (rather than Hebrew). But this too is neither unique, nor do all the Writing-books have such a feature.
Perhaps it has more to do with Ezra, and the final state of the books, which presumably he was largely responsible for. Note the final internal division (group iii below) of the books of the Writings:
Group I: The Three Poetic Books (Sifrei Emet)
1. Tehillim (Psalms) תהלים
2. Mishlei (Book of Proverbs) משלי
3. `Iyyov (Book of Job) איוב
Group II: The Five Scrolls (Hamesh Megillot)
4. Shir ha-Shirim (Song of Songs) or (Song of Solomon) שיר השירים (Passover)
5. Ruth (Book of Ruth) רות (Shavuot)
6. Eikhah (Lamentations) איכה (Ninth of Av) [Also called Kinnot in Hebrew.]
7. Kohelet (Ecclesiastes) קהלת (Sukkot)
8. Esther (Book of Esther) אסתר (Purim)
Group III: Other Historical Books
9. Daniel (Book of Daniel) דניאל
10. Ezra (Book of Ezra-Book of Nehemiah) עזרא
11. Divrei ha-Yamim (Chronicles) דברי הימים*
(*taken from Wikipedia page
Ketuvim - Wikipedia, the free encyclopedia )
There, you see, he could have been one that carried the completed
Daniel back from Babylon; and along with Chronicles (which is more than just a repeat of the Judean monarchical history: it is a theological interpretation of that history) which he very well may have been responsible for creating, completing, or editing, he is certainly mainly responsible for Ezra-Nehemiah.
But the idea that, for example, Psalms and Proverbs were not "canonical," or recognized as the Word of the Lord by believing saints going back to the earliest age they (or portions thereof) were recorded is simply not commensurable with our Lord's own attitude, or the attitude of the apostles about or unto revelation.
As to the interpretation of that passage, it is challenging but not past recognition. In my judgment, v26 stands alone, and describes the Messiah's (anointed One) rejection and death, followed by the consequence (the people of the prince who come and destroy).
v27 the recapitulates the same testimony (although I find the translation given above obscures rather than gives a good sense): Messiah comes and makes good the covenant promise, his ministry being about 3.5 years. When he is cut off midway, then the Desolator comes.
In this interpretation, which pretty well accords with EJ Young's view, the 70 Sevens are better understood as "prophetic periods or stages" rather than fixed and positive lengths of time, and back-to-back. The most compelling reason is that no truly satisfactory starting point and ending point, or intermediate break-point fixes precisely to the centuries between the exile and the Christ.
The important thing about the last "seven" then, is that it marks the Messiah's coming, and it only goes for half of it before he is cut off. This could indicate that the "last half" is never meant to be "counted up." Or it could refer to the 3.5 years that mark the Jewish Campaign of Vespasian-Titus, with a "generational reprieve" of 40 years, to give one last space for repentance. Or, thirdly, it could simply point to the fact that the initial ministry and death of Messiah only accounts for 1/2 of his mission, and the latter "half" is unending (kind of like the first divine Sabbath, Gen 2:2-3), or fulfilled in so different a way as that 3.5 of 7 doesn't do it justice by any human reckoning.