The 31-year old has departed BC Place after a year-and-a-half with the Whitecaps in exchange for a 2014 first-round draft pick and an international roster spot in 2013.
Hassli, who joined Vancouver from FC Zurich in March 2011, admitted it was a disappointment to be leaving but is now looking forward to a new chapter with the Reds.
"I was a champion in Zurich but we had almost 20,000 people every game in Vancouver, and when they sing your name, it's an amazing feeling," he said.
"That's why I was sad [Friday]. I was shocked. I had a great time here. I love the city. I love to play here. I want to say thanks to everybody. But that's part of the business.
"It was really two fantastic years for me, but I'm excited now to start in Toronto."