Michael Grabner and Pierre-Alexandre Parenteau also scored for Toronto, and Connor Brown had three assists.
Jonathan Huberdeau and Greg McKegg scored for the Panthers.
Toronto’s Jonathan Bernier made 32 saves. Roberto Luongo had 24 for Florida.
Kadri scored his 15th goal for a 2-1 Toronto lead on a power-play rebound at 10:36 of the second. He added another score on the man-advantage by patiently backhanding in a shot at 18:14.
Parenteau scored his 19th goal at 6:34 of the third on the power play for a 4-1 lead.
Kadri scored into the empty net with 2:39 remaining.
After missing a breakaway wide earlier on the penalty kill, Grabner scored his eighth off a 2-on-1 pass from Brown at 15:11 for the only goal of the first period.
The goal ended a drought of over 118 minutes by Toronto, which had last scored against Boston on Saturday and was shut out Monday in Tampa.
It was Toronto's second short-handed goal and the fifth allowed by Florida.
Huberdeau knotted the game 1-1 when he led a 2-on-1 and wristed his 16th goal through Bernier's pads at 6:23 of the second.
McKegg scored his first NHL goal at 11:26 of the third on a rebound.
NOTES: The Maple Leafs next play Thursday night at Buffalo. ... Florida will host the New Jersey Devils on Thursday night.