His new club, who are actually from Canada, are in their fifth season in the MLS, having been given a license to participate in 2007, and are coached by former Dutch international Aron Winter.
New York used Borman, along with teammate Tony Tchani, as make-weights in a deal to bring Toronto's Dwayne de Rosario to the club.
The 26-year-old Borman joined New York in 2008 from Rhode Island Stingrays and made 59 appearances over the next three years. He also started both New York's matches so far this season as a left-back, though he has also been used on the left side of midfield.
Borman, who was a junior with PSL side Santos, also went on trial at Argentine Primera División side Gimnasia y Esgrima La Plata at the end of the 2010 MLS season, but failed to win a move.
He will go straight into Toronto's squad for their game against Chivas USA on Saturday, with a win and a loss to their name so far this season.