He joined the Islanders as a free agent in 2008 and led the team in scoring his first season with 56 points (16G, 40A), while also representing the Islanders at the 2009 NHL All-Star Game. He was named the captain of the Islanders prior to the 2011-12 season.
Streit, who was originally drafted by the Montreal Canadiens in the ninth-round (262nd overall) of the 2004 NHL Entry Draft, is scheduled to become an unrestricted free agent July 5.
The Flyers and Streit's agent, Pat Brisson, have already started discussing a new contract, believed to be a four-year deal worth in the neighborhood of $4.5 million to $5 million per season.
A native of Englisberg, Switzerland, Streit represented his country in the 2006 and 2010 Winter Olympics, helping Switzerland to preliminary-round upsets of Canada and the Czech Republic.
Harper, 24, signed with the Flyers as a free agent on March 4, 2010.
In 143 games with the Flyers' American Hockey League affiliate, the Adirondack Phantoms, Harper recorded 20 goals and 21 assists for 41 points over parts of four seasons.