Butler has 20 goals and 28 assists in 128 games with Ottawa, New Jersey and Nashville. He had four goals and seven assists last season split between the Devils and Predators.
The Marlborough, Mass., native also played in 37 games with Albany in the American Hockey League last season, scoring 16 goals and adding 11 assists.
Brennan split last season between Buffalo and Florida, posting three goals and seven assists in 29 games. He also had 35 points (14 goals, 21 assists) in 36 games with AHL's Rochester.
The native of Willingboro, N.J., has four goals and seven assists in 40 career NHL games with Buffalo and Florida.