First clarify what adversaries mean by Church
To answer all this, first recall what the adversaries mean by "Church." That is essential for the real state of the question and for clearing away the ambiguity of the name.
Church is not here taken collectively for the whole multitude of the faithful who are and ever have been. The debate is not properly about that Church's authority.
Even though sacred Scripture's authority does not depend on the authority of the Church so taken, it is still certain that from that Church's testimony and consent can provide a divine, infallible argument for Scripture's authority that binds our faith — because that Church includes the Apostolic and primitive Church, whose role it was to confirm Scripture's Canon by a sure divine reason and hand it to the faithful as what would thereafter be faith's unique rule.
Latin
XXX. Ut omnibus his satis fiat, ante omnia hic est in memoriam revocandum quid Ecclesiae nomine intelligant adversarii. Id enim apprime necessarium est ad statum quaestionis probe intelligendum, & tollendam hic omnem homonymiam. Igitur sciendum est Ecclesiam hic non sumi collective pro tota multitudine fidelium qui sunt & hactenus fuerunt. Nec enim de istius Ecclesiae authoritate proprie quaestio est. Et quamvis Scripturae sacrae authoritas nequidem ex Ecclesiae sic sumptae authoritate pendeat, certum est tamen ex ejus testimonio & consensu duci posse argumentum pro Scripturae authoritate divinum & infallibile, & quod fidem nostram obliget: quandoquidem in ista Ecclesia comprehenditur Apostolica & primitiva, cujus fuit Scripturae Canonem certa quadam & divina ratione confirmare, & fidelibus tradere, tanquam qui deinceps esset unica fidei regula.