Before anyone goes into the validity of giving up so much for Doughty, who has 1 year left, this would come with some guarantee from Doughty on signing an extension with T.O.
Just can't input extensions into future years...

And, this only has $40m on the books for 2019-20. Giving Matthews 11.5, Doughty 10, and Marner 6.5 leaves the leafs at $68m in salaries for 2019 with an estimated cap of $82m for $14m in cap space.
Only have to fill out a few spots with that $14m. The salary structure is do-able.

Now this isn't me saying it's not an even trade cause I guess you can say it is... barely. Even if it is a guarantee he signs (which doesn't exist) as for the salary cap you didn't include salary bonuses or salary carryover and Horton needs to be on the roster on opening day. So your 8 mill in cap space goes down to about 5.5 million over the cap.

Well to make. it work cap wise, you would have to show how the 2018/19 cap works performance bonus and all. But these guaranteed extensions are silly. Yes silly. The Kings are not allowing the Leafs to negotiate with their star player to see if a deal works out. And if it doesn't Doughty has to go back to Kings, knowing his team doesn't want him.
Make a trade if you want, but these extensions, a year from when the contract end.....don't happen. "Some guarantee form Doughty". WTF does that mean. Nothing.

Doughty is a great defenseman, top 5 in the league. When I see trades like this, however, I wonder how a single player's presence would be the equivalent of having Nylander, Gardiner and Carrick on the team. It's too much, given that if he's interested in joining the Leafs, he could do so as UFA the year after.

Not to be over-critical, but I also have an issue with Emelin and Lethonen. We have an excellent backup acquired at low cost, Pickard, who's ready to play next year. Not to mention McElhinney who is still under contract. It's Babcock's decision to over-use Andersen, not the absence of reliable backups. As for Emelin, we have Borgman ready to play with a similar physical style, and with more offensive punch.

I just want to add how disgusting Nylander in a Senators jersey would look.

I don't know if Leafs haters or not, but in many posts the Leafs have to pay so much more for short term rentals than any other team. So many folks post trades, thinking playing value is the only criteria. Term is just a important in trades but is often ignored.