After submitting for the 2018 Major League Baseball draft but going undrafted, Stefanic compiled a résumé and highlight compilation and sent it to 150–200 executives from all 30 MLB teams. Stefanic signed with the Los Angeles Angels as a free agent in July 2018 after being contacted by Angels coach Chris Mosch, who was seeking a replacement for an injured player on the Arizona Complex League Angels team. He spent his first professional season in the Arizona League and with the Orem Owlz, batting .351 over 14 games. Stefanic spent 2019 with the Burlington Bees and Inland Empire 66ers, batting .282 with three home runs and 47 runs batted in (RBI) over 102 games. He did not play a minor league game in 2020 because the season was cancelled due to the COVID-19 pandemic. He started 2021 with the Rocket City Trash Pandas before being promoted to the Salt Lake Bees. Over 125 games between the two teams, he batted .336 with 17 home runs, 63 RBIs, and 26 doubles.
