Was the Greek version of Matthew originally written in Hebrew? If so, what impact does this have on the canon? For more information, see The Original Matthew.
2. What Was Original NT Scripture?
This is why the better answer is canon is the inspired words of the apostles when recollecting Jesus' words. For Jesus instructed them for 3 years. They were the only authors of true canon when recollecting Jesus' words. Interestingly, Greg, a highly conservative reformed writer, affirms this in 2015. At the same time, he tries to squeak in Paul, without telling you Paul never quotes Jesus in his epistles except  from the liturgry of communion and  one vision experience in 2 Cor. 12:7 that "my grace is sufficient for you" - Paul's Jesus denying Paul's request to be released from an "Angel of Satan."
The word "canon" means authority. That is, what are the authoritative works in themselves in the New Testament era that tell us about God and His plan for salvation? Before they were books for the New Testament, what was the canon?
Greg is 100% correct. Jesus said the 12 would recollect His words, and that is canon. Hence, you cannot squeeze Paul into this principle because Paul repeats nothing Jesus said except the liturgry which is lifted from Luke's gospel anyway.
This was part of the Hebrew Scriptures that Christians recognized from the time of Jude (60 AD) to 365 AD when it was dropped from canon. Might this have been wrongly dropped?