If one declines to accept as canon that which is of questionable provenance, one is in the company of numerous early Church fathers as well as quite a few figures within the Church right up to the Council Of Trent.
This is no more "Luther's Canon" than it is "Jerome's Canon." The Protestant Canon is that which is incontrovertibly scripture, relying upon authority going back to the early church and even before to rabbinical sources. The Catholic Canon has become "because we say so" despite the matter being left open theologically by the aforementioned Council.
Then you have just admitted that there is no way a Christian can be sure what is Scripture. The logical next step therefore is that there is no way a Christian can accept anything as inerrant and inspired by God. The next logical step is that there is there is no way a Christian can know what is Truth. The next logical step is that there is no knowable Truth, only that which each person left to their own interpretation and conscience accepts as truth, i.e. truth is relative.
In having no assure authority, we have come to where we are now, with Christians accepting abortion and gay marriage. All predictable results of the morass of theologies, ideologies and doctrines as seen in protestantism.
in other words, you follow Sacred Catholic Tradition!