McAvoy is brimming with excitement to get in a room with the best the U.S. has to offer, whether in management, coaching or players, to reacquaint himself with those he's met or played with in the past, to meet those he hasn't.
"You'll feel that immense sense of pride and push in the same direction to do something special together," McAvoy said.
And to help lead them.
It's something he's long dreamed about. Now it's here, with the 2026 Milano Cortina Olympics on the horizon.
"Between the Stanley Cup, and when you were a kid it was the World Juniors, it was the Olympics," McAvoy said. "Those were everything you dreamed of as a kid and wanted to be a part of and do. This is definitely a step in the direction for that. You're seeing this stuff unfold in front of you, all the stuff you've worked for.
"I couldn't be more excited, and then obviously it's a huge honor to be named one of the leaders, and it goes without saying this team is full of leaders and guys that you want to follow into battle. So we'll all pull on that."
It will help, Sullivan said, that one of the three players in his leadership core is one with whom he's so well-acquainted, someone with whom he's already built confidence, crucial in a short tournament like the 4 Nations.
"I think anytime you have an opportunity to build relationships with people, it helps," Sullivan said. "Because you know them on a deeper level. You know their character. You know what makes them tick. There's certain barriers that you don't have to break down from a trust standpoint that already exist. I think trust is such an important element with respect to a player/coach relationship, and that takes time."
But before McAvoy and Sullivan reconnect in Montreal, there are a few more pressing issues for the defenseman.
He needs to get his diaper changing technique down.
It has been a whirlwind of a first 10 days, even with a registered nurse in the house. Kiley, who went to nursing school, had done a circuit in labor and delivery. Even that didn’t prepare them.
"You think you might know what to expect, but you don't," McAvoy said. "Just the amount of pride and the absolute, utmost respect and love for the moms and what they do. Because it truly is incredible. I've seen that just on a three-day scale, how much they put their bodies through and what they go through. She's doing an incredible job."
They have been surrounded by love, by McAvoy's parents, who are first-time grandparents, and by his sisters, first-time aunts, including Kayla, an assistant sports scientist for the Rangers.
It has been a time of celebration, of recovery, an uplifting time for McAvoy, in a season that has not been easy for him or the Bruins.
The defenseman had come into 2024-25 with a sense of purpose, having spent last summer thinking about it being time for the new leadership core of the Bruins to win, time for them to step out of the shadows and into a new era.
But the season has fallen flat.
Instead of being a shoo-in for the Stanley Cup Playoffs, as the Bruins have been in every one of McAvoy's eight seasons in the NHL, they are a question mark. They have been hovering between third in the Atlantic Division and the two wild card spots, sometimes falling out of playoff position entirely.
They currently are tied with the Tampa Bay Lightning, who have played three fewer games, for the second wild from the Eastern Conference.
It is a tenuous spot.
"This year, it's had its trials for sure, more than any other year," said McAvoy, who has 22 points (seven goals, 15 assists) in 48 games and is one point away from becoming the eighth Boston defenseman with at least 300 career points. "You can look at it one of two ways. Like, one, this stinks. We were expecting to be somewhere different. … And everybody that I've talked to, we've had it very good. I have a lot of friends, a lot of people that have never played in the playoffs. A lot of teams that go through it.
"So I've been looking at it in the scope of, this is good for us. Grand scheme, long term, these are things that you go through that make you stronger. You find out more about yourself, more about your group, more about how to lean on each other. Support systems. Because it's not all sunshine and daisies, even though it has been for a couple of years, throughout the regular season. That's the lens I'm taking and I'm looking through is just that all of this will lead to something good in the future."