The Rovers duo are in the 18-man squad that has travelled for the international friendly match against the Danes in Fredericia.
O'Connor had a strong season on loan with League Two side Burton Albion. The defender was an ever-present at right back as the Brewers made the play-offs only to lose to Bradford City over two legs.
O'Sullivan's season ended on a high as he made his first senior appearance for Rovers. The midfielder coming on as a second half substitute in the final game of the 2012-13 campaign away at Birmingham City.