Leafs and the Playoffs?

Are the Toronto Maple Leafs a playoff contender this season? They've managed to play tight games against some of the best teams in the league (one goal games with Montreal) and it seems like every time they lose, they dominated the game, whereas when they win, they were dominated. If they can figure out all the defense nonsense, this team will look really scary. Look at the Maple Leafs' lineup as of now.

Forwards

Zach Hyman          Auston Matthews          Connor Brown

                           James van Riemsdyk        Tyler Bozak              Mitchell Marner

                                  Leo Komarov            Nazem Kadri            William Nylander

                                    Matt Martin               Ben Smith               Nikita Soshnikov

Defense

Morgan Rielly          Nikita Zaitsev

Matt Hunwick           Roman Polak

Jake Gardiner           Connor Carrick

Goalies

Frederick Andersen

Jhonas Enroth

So how do you improve this team? The defense just sticks out like a sore thumb but fixing it will be a challenge. The average age of this team is around 25 years old. That makes them the youngest team in the NHL. If you want to improve, you have to think about that. We cannot start trading young prospects for single year defensive improvements, you need to stay young, Morgan Rielly and Nikita Zaitsev have been great but we need more. Sadly, young defensive players are really rare and their teams know that. Obtaining young, talented defensive players will be very hard and if the Leafs don't find any soon, the playoff push will be lost.
I've seen rumours about Peter Holland being on the market for a "shut down defense man" but I don't really know if that is true. He is being paid 1.3 million dollars and I don't know if anyone is willing to take that on for a potential 15-20 goal scorer. To make matters worse, the most logical choices for defense men have recently signed (Trouba and Lindholm) so I wonder who the Leafs' management are targeting.