There’s a wonderful series of trails in southern St. Catharines in the area of Brock University, making for some scenic, easy trail running around the park-like campus, a quarry, and a lake. Use the Bruce Trail  — the 900 km walking/hiking trail in the Niagara area — as the anchor. Begin by exploring the park-like campus of Brock University, which itself  is part of a nature preserve. There are some nice trails on at the northern end of campus, including a cross-country course, and connections to the Twelve Trail.  Take the Bruce Trail east for 1.5 km to Glenridge Quarry, a recreational facility built on a former landfill. A loop around its trails is ~2 km.

Bruce Trail @ Lake Moodie. CC 2.0: veggiefrog

For a longer run or another option, take the Bruce Trail south of campus to Lake Moodie. It’s a fairly easy trail run around the lake for up to 6 km to Decew Falls. There are several km of additional trails in the area — some easier, others more rugged.

Add-Ons: The Twelve Trail heads north along Twelve Creek for 5 km to downtown St. Catharines. Just west of Lake Moodie, there’s extensive trail running options in Short Hills Provincial Park.