Guenette signed with the Penguins in 1985 after two seasons in the Ontario Hockey League with the Guelph Platers. He remained in the OHL for one more season in 1985–86, where he led the Players to the J. Ross Robertson Cup title, and then the 1986 Memorial Cup championship. Guenette won the Leo Lalonde Memorial Trophy as the OHL's top over-ager, as well as the Hap Emms Memorial Trophy as the top goaltender in the Memorial Cup, in addition to being named to the Memorial Cup All-Star team.