>>1728523go big or go home
day 1: from the garden/JBL take orebed brook trail up saddleback/basin/haystack. then dip down behind haystack and take bartlett ridge down to marcy brook and set up camp overnight at the brook.
day 2: take elk lake-marcy trail up the south side of marcy (snag mount skylight on the way), then take hopkins or phelps trail (hopkins is less steep) back to the JBL
You'll see some people up around marcy and the JBL, but you'll avoid the biggest crowds that will be around algonquin and marcy dam - and worst, the ADK lodge.
If you want to get an early start after driving from toronto there's a couple hostels in keene valley that will put you right close to the garden trailhead.