De Thomasis also ventured into the business side of soccer, where he purchased the York Region Shooters of the Canadian Professional Soccer League. He eventually solidified the franchise into a powerhouse within the league. He also managed the team for several seasons, and achieved significant results by winning the CSL Championship in 2006, and 2017. In 2018, he briefly was associated with Filipe Bento's organization Unionville Milliken SC, and placed the team into League1 Ontario.
De Thomasis initially became involved in soccer by coaching at the youth level.[11] In 2002, he purchased the York Region Shooters franchise in the Canadian Professional Soccer League from Frank Bisceglia.[12] The following season the Shooters merged with the Vaughan Sun Devils to unify the York Region territory with De Thomasis becoming the principal owner.[13] After the acquisition Vaughan reached the CPSL Championship final in four consecutive seasons, and clinched their first piece of silverware the Eastern Conference title in 2005. In 2005, he was awarded the CPSL Commissioner's Award.[14]
As part of the reforms conducted by CSL Commissioner Cary Kaplan the Vaughan Shooters became inaugural members of the International Division, and were renamed the Italia Shooters in 2006.[15] Throughout the season De Thomasis undertook the coaching duties, and claimed the organizations first championship title, and was recognized by the league with the Coach of the Year Award.[16][17][18] In 2010, he received the Harry Gauss Memorial Award for his continual allegiance, commitment and support to the league.[19] In 2017, he managed York Region to their second championship title.[20]