Peel police made the arrest, but there has been no confirmation of which brother, Curtis or Corey Murray, is in custody at 23 Division.
Seraphine was found suffering from multiple gunshot wounds at an Etobicoke apartment complex early on March 21. He was later pronounced dead in hospital.
On Monday, police described the Murray brothers as dangerous and warned they may attempt to flee the country.
Det. Tam Bui said Curtis Murray, of Brampton, has a "long criminal record" that includes assault with a weapon, sexual assault and extortion.
His brother, Corey, said Bui, is wanted for violating parole and on various warrants from Peel Regional Police, and has been on the run since March 2014.
Trevor Seraphine was a shy boy, sister says
Xabie Seraphin, Trevor’s sister, spoke briefly at the emotional news conference.
"I just want to know why these guys killed my brother," she said, before breaking down into tears.
She described her brother as shy, but said he had lots of friends. He wanted to be an engineer. He also loved to rap.
As tears rolled down her cheeks, Seraphin said her brother "didn’t even get a chance to live,"
An online fundraiser, meanwhile, is attempting to raise enough money to bring Seraphin's parents, who live in St. Lucia, to Toronto for the burial.
Police encouraged the public to donate to help the family.
Block sale items
Police said Monday they were also looking for items bought during a block sale at that same apartment building, 44 Willowridge Dr., one day prior to the shooting.
Bui said items at that sale are evidence in the case, and whoever has them is asked to take them to 23 Division.
"You are not in any trouble. You will not face any criminal charges," Bui said. "You will only be assisting Trevor's family."