The annual tournament is always a test for Canada because many top players are still involved in playoffs with their junior clubs.
A team led by Kootenay Ice forward Sam Reinhart and 16-year-old phenom Connor McDavid of the Erie Otters will be seeking Canada's first gold since 2008.
The tournament begins Thursday at the two 2014 Olympic rinks in Sochi, Russia, with the United States seeking a fifth straight gold medal.
"It's a great challenge," said 59-year-old Hay. "You start with one group, then you add players as teams get eliminated from the playoffs.
"The challenge is to continue to grow as a team and to embrace the new players coming in."
The most recent additions were Owen Sound Attack stars Zach Nastasiuk and Craig Bigras, both ranked in the top-33 for the June NHL draft by NHL Central Scouting.
Madison Bowey of the Kelowna Rockets, Carter Verhaeghe of the Niagara IceDogs and Nicolas Baptiste of the Sudbury Wolves are to arrive this week but won't be available for Canada's first game Thursday against Slovakia.
Hay did not want to discuss the players who couldn't come because of playoff duty, including top juniors like Nathan MacKinnon of the Halifax Mooseheads, Aaron Ekblad of the Barrie Colts and Max Domi of the London Knights.
A finger injury has also deprived the team of six-foot-five defenceman Darnell Nurse of the Sault Ste. Marie Greyhounds, considered to a be top-10 or even top-5 draft prospect.
With its full cast of players for the under-18 Ivan Hlinka tournament in August, Canada won gold with MacKinnon scoring a hat-trick in the final against Finland. Reinhart, who is only eligible for the 2014 draft, was captain of that team and will wear the C again in Sochi.
Hay prefers to focus on the players on hand, who are a promising group in themselves.
Some key players could be defencemen Josh Morrissey of the Prince Albert Raiders, returning from last year's team, six-foot-six Samuel Morin of the Rimouski Oceanic and Shea Theodore of the Seattle Thunderbirds.
Up front, soft-handed six-foot-five centre Frederik Gauthier of Rimouski, who is ranked seventh among North American skaters by NHL Central Scouting, Morgan Klimchuk of the Regina Pats and Laurent Dauphin of the Chicoutimi Sagueneens can do some damage.
The speedy McDavid is the early favourite to be drafted first overall in 2015.
Whether he is ready to play a prominent role against players two years ahead of him on the world stage at the U18 remains to be seen. The Newmarket, Ont., native is the second youngest to play in the tournament for Canada after John Tavares in 2006.
With Erie this season, McDavid had 25 goals and 66 points in 63 games and was named OHL rookie of the year. Not bad for a guy who was 15 when the season started.
"I hope he learns a lot and it turns into a prominent role," said Hay. "He's shown in the Ontario Hockey League that he's a real talented player who can be counted on."
Hay will need to decide the starting goaltender among Philippe Desrosiers of Rimouski, Austin Lotz of the Everett Silvertips and Spencer Martin of the Mississauga Steelheads.
Canada won't be the only team missing players because of junior playoffs.
Host Russia is without Kirill Vorobev of the Portland Winterhawks and Nikita Zadorov of the Knights. The Rouyn-Noranda Huskies still have forwards Nikita Kucherov of Russia and Sven Andrighetto of Switzerland.
And Russia's top prospect, Valeri Nichushkin, may join the team late because of KHL playoffs with Traktor Chelyabinsk.
The Russians open Thursday against the U.S., which gets most of its players from its national development program.
"I suppose our fans will be a big plus for us, but it means our team will have big responsibilities," coach Igor Kravchuk told the IIHF website. "Also, the under-18s in Sochi will be a test competition before the Olympics. This means our team will be under big attention."
Canada will play the first round in Group B against Slovakia, Germany, Switzerland and Sweden at the 7,000-seat Shayba Arena.
Russia and the U.S. are in Group A with Latvia, Finland and the Czech Republic at the 12,000-seat Bolshoy Ice Dome.
The semifinals are on April 26 with the final on April 28.
A new format has the top four teams in each group advancing to the quarter-finals. Previously, first place teams got a bye to the semis.
Canada won gold in 2003 and 2008 but then was out of the medals until it took bronze at last year's U18.