The church did not declare the canon of Scripture, but they confessed what was from the apostles. Similarly, the church does not declare doctrine, they can only confess what was already revealed.
One cannot exist without the other for the declaration of the canon of Scripture is in itself a question of doctrine.
The belief that apostles had authority to declare doctrine, and the judgement of what was authentic from the apostles, does not equal the authority of the apostles.
Now if this authority existed in the past it must continue to exist today.
If I recognize the authority of the apostles, that does not mean I have the authority of apostles. Recognizing the authority of the apostles is doctrine. Collating their authenticated works is not doctrine.
This is outside of Scripture. Thus you concede we must look outside of Scripture to know what is Scripture. If the church is reliable in this area then it must also be reliable in teaching doctrine.
Similarly, the church does not declare doctrine, they can only confess what was already revealed.
That doctrine is Catholic. See St. Ignatius and Justin Martyr.
The belief that apostles had authority to declare doctrine, and the judgement of what was authentic from the apostles, does not equal the authority of the apostles.
But who can make this judgment?
Collating their authenticated works is not doctrine.
Authenticating what are their works, and thus Scripture, is doctrine.