Unknown to most locals even, Guelph sports a hiking trail that cuts through the heart of the city, extending from Preston to Limehouse (where it meets the Bruce Trail). The easiest place to pick up the trail is near the covered pedestrian bridge. There's some parking at the York Road entrance to the park there. I like to take the trail southeast from there, you'll cross several streams aside from the ironically named Speed River. It's a busy trail so you won't be alone especially on weekends, and a cell phone works for almost the whole length of the train.
For more information, check out their website here.
Not to alarm anyone, but Southern Ontario is now home to West Nile. As a general rule, when hiking bring insect repellant that has DEET and wear both long pants and long sleeved-shirts.