De Guzman, a 31-year-old from Scarborough, Ont., amassed two goals and eight assists in 65 MLS matches with Toronto, which signed him as its first designated player on Sept. 11, 2009.
Prior to joining the Reds, he spent four seasons playing in Spain for Deportivo la Coruna — the first Canadian to play in La Liga — and earned team player of the year honours in 2007-08.
"Losing someone like Julian is never easy," Toronto head coach Paul Mariner said in a statement. "But this deal gives us increased flexibility to address areas where we have more pressing needs."
De Guzman, who is making $1.9 million US in the final year of his contract, was one of three DP players on Toronto — the others being Torsten Frings ($2.4M) and Danny Koevermans ($1.5M) — and trading him "opens up a designated player spot on our club," Mariner said.
"He [de Guzman] will give FC Dallas an additional veteran that can solidify our possession style of play," Dallas head coach Schellas Hyndman noted. "He also has a bit of toughness to him that will help us win 50-50 balls and control the central midfield."
'A very skillful player'
De Guzman began his professional career in Germany with second-division side FC Saarbrucken in 2001-02, then moved to Hannover 96 of the Bundesliga for three years.
Although De Guzman returned home amid much fanfare, he endured an uneven tenure with Toronto and never truly lived up to expectations, seeming to fare better in international play than in Major League Soccer.
"Julian has had a very experienced career," Hyndman said. "He is a central midfielder, a holding midfielder and a very skillful player.
"He also has a lot of experience playing with the Canadian national team."
De Guzman has tallied four international goals in 56 appearances since making his debut with Canada's national squad at the 2002 Gold Cup against Martinique.
In Wiedeman, Toronto gets an affordable 22-year-old Generation Adidas forward — he reportedly makes $123,000 US — selected in the second round (21st overall) of the 2010 MLS SuperDraft.
The Oakland native failed to score in eight matches with Dallas.
No Wahl on Impact
The Montreal Impact made a move as well, unloading American defender Tyson Wahl on the Colorado Rapids for an international roster spot in 2014.
"He was very committed and showed a lot of leadership to this organization," Impact head coach Jesse Marsch said of Wahl, playing in his seventh MLS season.
"Although it wasn't always easy for him during his stay, he remained a true professional from the first day," added Impact sporting director Nick De Santis.
Wahl, 28, made 11 starts for the Impact, plus two more in Amway Canadian Championship matches.
He was acquired by Montreal from the Seattle Sounders for allocation money last Nov. 23.