2009-10: Daniel Altshuller split the goaltending duties for the Ottawa 67s midget minor team with Gian Marco Demeis. He was 12-0-2 with four shutouts and had a 1.71 goals against in 16 games. Ottawa finished second to the Ottawa Valley Titans in the regular season. In seven playoff games he was 3-2 with a 4.34 goals against. Altshuller was a third round selection (45th overall) of the Belleville Bulls in the 2010 OHL Priority Draft.
2010-11: Altshuller played 43 games for the Nepean Raiders in the Junior A Central Canada Hockey League in Ontario. He finished with a record of 19-13-10 and a 3.22 goals against and .906 save percentage. Nepean finished fourth in the CCHL's Yzerman Division. Altshuller played all seven games in Nepean's playoff series with Brockville and was 3-4 with a 3.73 goals against and .911 save percentage.
2011-12: Oshawa obtained the OHL rights to Altshuller from Belleville in August and he played 30 games for the Generals in his first OHL season. Splitting time with 20-year-old Kevin Bailie, he was 11-19 and had a 3.55 goals against and .900 save percentage. Oshawa finished third in the East Division and lost in the first round of the playoffs. Altshuller appeared in five of six games during the Generals playoff series with Niagara, starting four of them, and was 2-2 with a 3.87 goals against and .918 save percentage. Altshuller was ranked 12th amongst North American goaltenders in Central Scouting's final rankings prior to the 2012 NHL Draft and was selected by Carolina in the third round (69th overall) of the 2012 NHL Draft.