Leeb opened the scoring with a shorthanded goal 3:09 into the game and added a power-play goal midway through the second period to pace the Marlies (2-2-1-0). Eric Westrum and Colin Murphy each added a goal and an assist while Jeff Corey also scored for Toronto.
Kris Newberry and Chris Harrington had two assists apiece in a winning cause.
Corey Locke led the way offensively with a pair of goals for the Bulldogs (1-3-0-0), who have lost three straight. Mathieu Roy and Maxim Lapierre had singles for Hamilton.
Hamilton was 2-for-9 on the power play while Toronto went 1-for-7 with the man advantage.
Mikael Tellqvist earned the win for the Marlies with a 29-save performance. His counterpart, Yann Danis, stopped 28 shots for the Bulldogs.