There's Boyd Park just south of Rutherford on Islington. Lots of trails around the perimeter of the park. If you follow the river north and cross Rutherford, there is a path that goes north all the way to Kleinburg (Teston Rd). On Pine Valley, just north of Rutherford is Kortright Centre. If you have ay map or GPS, you could hike through a bit of brush to some cross country ski/walking trails in Kortright.
North of there, is the Oak Ridges Moraine Trail, north of 15th/Bloomington Rd - the easiest access is by the old Eaton Mansion on the Seneca College property. It's a huge trail system stretching from Markham to Caledon.