I remember jumping - diving off the docks at camps in Point Au Baril in July and August, that surface water was comfortable, but once you got down 6-8 feet it was like hitting an ice cube! Lake Ontario is a deep lake, it's going to take some time for anything other than the first few feet of surface waters to warm up?
Lure choices? any steelhead I kept for a meal here was stuffed with baitfish, minnows, shad, small perch, something that imitated them would be my choice.