There’s some nice running in Darlington Provincial Park, located in the southeast part of Oshawa. The park is located on the banks of Lake Ontario and is known for its sandy beach, nature trails & camping/picnic facilities. For running, there’s ~5 km of running on scenic nature trails and a section of the Waterfront Trail that runs through the park. It’s a scenic combination of marsh ecosystem, fields & meadows, some forest, and a section along Lake Ontario. In summer, go for a post-run dip in Lake Ontario!
For a route, using this trail map, we recommend using the Waterfront Trail as an anchor, and combining the McLaughlin Bay Trail, Burk Trail, and Robinson Creek Trail.