How can we know the Bible is God's Word unless someone (the Church) tells us it is?
The church testifies that Scripture's 66 books are authoritative, but it does not make them so. Scripture is self-authenticating (2 Tim 3:16), and does not need an external authority to make them authoritative. A minister doesn't make a wedding by his authority, he announces that it happened and is now true; same with the church speaking of Scripture.
Doesn't the apostles' verbal or oral-tradition authority continue in the Church? See 2 Thessalonians 2:15 - "So then, brothers, stand firm and hold to the traditions that you were taught by us, either by our spoken word or by our letter."
Apostolic authority continues only in Scripture, with the close of the canon, not with oral traditions as well. When the apostles died, they did not pass on authority to heal or to make verbal pronouncements equal to scripture - this is inferred from 2 Cor 12:12. The signs that marked apostles are not done by the pope or by supposed miracle workers today. (God certainly heals today, but no longer gives certain individuals the gift of healing, as he gave apostles.)
That a Roman Catholic can love the Scriptures doesn't disprove sola scriptura.
Which is the ultimate authority: the Bible, or the Church?
Protestants say the Bible. Rome and Eastern Orthodoxy say the Church.