As good as we've been, it will still be *somewhat* of a challenge to make the playoffs. In the Atlantic there are 6 potential playoff teams (Toronto, Boston, Detroit, Tampa, Montreal and Ottawa), but 1-2 will have to miss the playoffs, I don't think anyone is a true lock to make the playoffs in the Atlantic.
With that being said, if I had to guess I'd have us finishing 2nd-3rd in our division, with Boston and Detroit occupying the other 2 top 3 spots. We'd then face either Boston or Detroit in the 1st round, and could definitely beat either one, though I think we'd be slight underdogs against either of those teams. We're good enough to have at least a decent chance against any team in the league though, so as long as we make the playoffs, who knows how far we go!
If you assume we have a 90% chance to make the playoffs, then a 45% chance to win any given series, this would be the probabilities of each of the OP's options:
3.7% - Leafs win the cup
4.5% - Leafs lose in the stanley cup final
10.0% - Leafs lose in the eastern conference final
22.3% - Leafs lose in the second round of the playoffs
49.5% - Leafs lose in the first round of the playoffs
10.0% - Leafs miss the playoffs
Based on this I voted "Leafs lose in the first round of the playoffs", but really we could end up anywhere if we make the playoffs.