That truck stop (Fifth Wheel) in Bowmanville, maybe your best bet for early service (open 24 hours) and convenience, assuming you are traveling the 401.
At the Thickson exit in Whitby there is the Halibut House, have a pretty good breakfast but open later than you might like (8am I think). Dine's on King Street in Oshawa opens at 7am, about 5 minutes north of the 401 at the Stevenson exit. http://dinesrestaurant.com/ . Wally's World in Oshawa is open 24 hours but a bit north of the 401 on Simcoe, south of Taunton. http://www.wallysworld.ca/index.html . There are a couple of places in Bewdley but not sure they open too early. Rhino's opens at 8am.