Dickey becomes part of a stellar rotation that includes Johnson, Buehrle and returning starters Ricky Romero and Brandon Morrow.
Thole gives the Blue Jays a catcher who is familiar with handling Dickey's knuckleball. He joined a lineup that features former home run champ Jose Bautista and Edwin Encarnacion, who hit 42 homers last season.
D'Arnaud turns 24 in February. He hit .333 at Triple-A Las Vegas with 16 homers and 52 RBI before tearing a knee ligament trying to break up a double play in June. He has been an All-Star at several levels during his climb through the minors.
The Los Angeles Angels and Texas also were also interested in Dickey.
Popular with Mets fans, Dickey perturbed team management when he spoke about his contract situation last week during a club event at Citi Field for children displaced from their schools by Superstorm Sandy.
Dickey said he enjoyed playing for the Mets and added it would be "disappointing" if he went through his option year without a new deal and became a free agent.
"If that's the decision that they make, I feel like it would be unfortunate because it probably is going mean that I'm not going to be back," Dickey said then. "And that would be sad."
Buck was an All-Star with Toronto in 2010. The 32-year-old hit .192 with 12 home runs and 41 RBI for Miami last season, then was part of the big trade between Marlins and Blue Jays.
The 20-year-old Syndergaard went 8-5 with a 2.60 ERA for Class A Lansing. The 18-year-old Becerra hit .250 with four RBI in 11 games in the rookie Gulf Coast League.
Thole hit .234 with one homer and 21 RBI in 104 games last season. The 26-year-old played four seasons with the Mets.
Nickeas split last season with the Mets and Triple-A Buffalo. The 29-year-old hit .174 with a homer and 13 RBI for New York.