I take the Glen Erin trail which leads to the junction of the Sawmill valley trail and Mississauga road. I cross Miss. Road, go down the hill into Erindale park and then I follow credit river alongs the Culham trail.
Except for the few breaks in the Culham trail (street sections), you can go all the way to Creditview and Britannia. And I think it goes a bit further than that.
Warning: The Sawmill valley trail is not paved. Most of it is on dirt with some areas with large gravel which narrow tires will get stuck in. The Glen Erin trail is paved all the way from the start near Winston Churchhill and 403 to the end. The Culham trail is a mix of paved and gravel.
Oh and... the Burnhamthorpe trail runs across all 3 mention trails. At the western part it intersections the Glen Erin trail. Then just west of mississauga road it intersects the Sawmill Valley trail (entry point is to the north east of the trail, a bit confusing). Then the Burnhamthorpe trail crosses the Culham trail on the north east side just past the bridge. Take the entrace to riverwood but go down, not up. You can still join up by going North though but you'll have to find the trail entrace in back of the buildings.
As far as I'm concerned this "triangle" is the best part of the complex of trails in Mississauga. Glen Erin, Sawmill valley, Culham and Burnhamthorpe.