Left-winger Obadeyi started his career with Bolton but made only four appearances and went on a succession of loan moves.
The 24-year-old moved to Rio Ave in 2012 and made 12 appearances in the Portuguese top flight before returning to north-west England to sign for Bury the following year, although he spent most of last season on loan at Plymouth.
Magennis was released by Aberdeen in the summer after playing 123 matches in four years at Pittodrie.
The Northern Ireland international scored 12 goals for the Dons and made most of his appearances from the bench, playing up front, on the wing and at right-back.
The 23-year-old ended last season on loan at St Mirren, failing to find the net in 13 games.