Out of curiosity I just made a rough estimate of what the Leafs cap hit next season would look like, assuming they don't trade, sign, or buy out anyone (except Cowen), and replaced all their UFAs with players on ELCs. (I guessed at the cap hit of their RFAs based on production / current salary / comparables).
Should be around $67M (that includes Horton's $5.3M).
The cap ceiling is $71.4M this year, and it's probably going to be about the same next year assuming the players use the escalator.
That gives them, at most, ~$11M for UFAs aka Stamkos
If they want more cap space next year they're going to have to find a way to trade Greening ($2.65M) or Bozak ($4.2M), or perhaps buy out Laich ($4.5M, with buyout cap hit $1.83M next year)