Sundin, the Leafs' captain, has missed three straight games since an injury to his lower body in Game 4.
He took part in Tuesday's morning skate, but Toronto coach Pat Quinn didn't expect him to play.
Sundin has a goal and three assists in four playoff games. He had 31 goals and 44 assists in 81 regular-season games.
Ottawa beat Toronto 2-1 in overtime Sunday, forcing the deciding game.