Step Four - the Big Dawg
The Leafs aren't going to get a better chance at winning the Cup than this year. Chris Tanev, Morgan Rielly, John Tavares and Jake McCabe are as good as they'll ever be. Marner might be on his way out, and who knows how long this goalie combo is good for before they turn into pumpkins?
The time to try and win is now, and the best way to do that is with a huge move for an impact player. Unfortunately, the Leafs are extremely limited by their lack of cap space. The only reasonable acquisition here is Bowan Byram of the Buffalo Sabres.
He's 23, he's recently performed at a level which could reasonably translate to being the number-one guy on a contending team, and he's a pending free-agent on a bad team that won't make the playoffs, and he only has a $4 million dollar cap-hit.
Byram would allow the Leafs to use Rielly/OEL as a killer third pairing that they can pick their spots with. They could pair Byram with Timmins and stick with the Tanev/McCabe line that has worked so well for them. It would be a substantial upgrade to a blue-line desperate for more puck-moving talent, and while it would likely cost Easton Cowan, it's a trade worth doing for the Maple Leafs who really don't have a lot of options when it comes to finding a number-one defenseman they can afford and who would potentially be available.
Whatever the lines end up being, the Leafs would be able to pair Domi/Matthews, Tavares/Marner, and Gourde/Nylander, which would eliminate their depth scoring issues, and make them a lot harder to play against. Competition for the last three top-nine forward spots would be between Knies, Robertson, McMann and Pacioretty, which could only help the Leafs.
By only making two trades - which they could realistically do - the Toronto Maple Leafs can turn themselves into the best team in the NHL and overcome their two main weaknesses - which are a bad blue line and a lack of depth scoring.