According to James Myrtle and Jonas Siegel of The Athletic, The Maple Leafs were the runner-up in the Jacob Markstrom sweepstakes and their 1st round pick was a part of the package offered to acquire him.
Following the Markstrom trade, the Leafs signed young goalie Joseph Woll to an extension, though it cannot be made official until July 1st. Even though Woll has been extremely impressive when he's in the net, his health has held him back from becoming a true number 1 goalie. He'll have anorher opportunity to establish himself as one this season.
Now that we know that Treliving is open to moving the pick, it opens up the possibility of filling a significant area of need via the trade market as opposed to just trying to plug holes in free agency.
The Leafs may not necessarily spend their first round pick to acquire a goalie, they could instead opt to use the pick in a package to try to acquire another high-end defenseman. We'll see how this all unfolds over the next few days with the draft and free agency coming up imminently.