Depending on your comfort level in traffic, you can shoot straight down Leslie. You just need to watch your lane placement as you go under the 401. It's the fastest southbound route. I used to ride it daily when I worked at Steeles and leslie.

Using the park system, you enter the southbound stretch just north of North York general at the southeast corner of Leslie and Sheppard. Once you're on the path, head south where it ends at Duncan MIlls. On this route there are some wood bridges that get very slippery when wet. If you live south of Sheppard, you can get on this via Havenbrook or Manorpark before it crosses under the 401.

Go west on Duncan Mills, south on Valleybrook turning left onto Lesmill and on south to York Mills. Go west on York Mills over the bridge and taking an immediate left at the light onto Scarsdale blvd. If you time your turn onto York Mills right, it's often easiest to move left right away and ascend the bridge in the left lane. From Scarsdale you can go west on Bond or further south, but you'll eventually head west to Leslie. You can go across Rippleton park to Banbury or just head down Leslie at this point. You can either go in at Edwards Gardens' but I usually just head down Leslie and enter the park system via the Wilmott creek entrance off of Leslie (sort of in the dip before the last climb before you descend to Eglinton on the right). It's not marked. The path down from Edwards gardens was pretty munched the last time I was through and the hill down from Leslie, you're supposed to walk your bike.

Leslie and Eglinton is an ugly corner with a right turn lane that people will squeeze you in and a vanishing right lane as you do the exhaust inhaling climb West up Eglinton. That's why I enter at Wilmott creek. Once you're in Sunnybrook park you can head over and ascend to Broadway. You'll head south, then turn right then left into a parking lot on your left. There's a metal bridge that crosses and a path that ascends to Broadway (spin baby spin). Head west across Broadway. You can go the whole way crossing onto Montgomery, south along the community centre, crossing Eglinton at Lascelles. Head south, left on Kilbarry, south on Russel Hill Road and there you go pretty much. This will take you to the Davenport lanes or down to Dupont as you prefer.

This route is pretty much the one marked on the city bike map. It's a nice ride and the park is sweet once the trees start to turn. Watch for people walking five dogs, moms with double wides walking three abreast (not kidding) and the other vagary hazards of the multi-use park system.

[edit] Waa, too long to type that. I'd suggest jumping out the park system a little earlier and heading
West on Broadway. Once you're down Russell Hill Road, you can jump over to St. George (right on Dupont, quick left) and head south to Dundas, left to get to McCaul. You can make it a little quicker heading south on Sutherland from Broadway, west on Moore, then down Inglewood to St CLair and then west.