The LXX Septuagint canon predates it by about 350 years and is still used by Ethiopian Jews to this day.
The Septuagint wasn't a "canon", it was a collection of books translated into Greek for those Old Testament books that were in Hebrew. Most of the extra books (Apocryphal) were originally written in Greek. It was used mainly by Alexandrian Jews who spoke Greek. If you are presuming that a book's presence in the Septuagint meant it was part of the Old Testament canon, then why were only seven of the FIFTEEN extra books added to the RC canon and not all of them?