Substitute Nick Soolsma, positioned in the centre of the penalty box, headed a Ryan Johnson cross down to Lambe, and the Bermudian danced left and right before firing a right-footed shot past Joe Cannon.
Toronto players poured into the southeast stand at BMO Field after the win to celebrate with their fans.
The two teams tied 1-1 last week in Vancouver, with Johnson's goal for TFC followed by a magnificent volley by Eric Hassli in stoppage time for the Whitecaps.
Vancouver showed little in a poor first half Wednesday. But there were fireworks early in a wild, ill-tempered second half as both teams had a man sent off — Julian de Guzman for Toronto and Sebastien Le Toux for the Whitecaps.
The ejections made for a wide-open finale to the final which also saw an 81st-minute goal by Soolsma whistled for offside. Toronto outshot Vancouver 13-4 (3-0 in shots on target).
Toronto wins the Voyageurs Cup for the fourth straight year, providing a sliver of optimism in a dismal season to date. Wednesday's result also means that the worst team in Major League Soccer is now No. 1 in Canada.
Loser of all nine league games this season, Toronto has shown another side in cup competition. The team is 3-1-4 in combined CONCACAF Champions League and Canadian Championship play.
For Vancouver (5-3-3 in league play) it was a disappointing end to its bid for a trophy.
The second-half ejections show the kind of tension that the Canadian championship can produce.
In the Toronto-Montreal semifinal, Impact coach Jesse Marsch and then Toronto assistant Bob de Klerk had to be separated at the end of the second leg at BMO Field.
On Wednesday, De Guzman was shown a straight red in the 57th minute, seemingly for a punch in a melee as players jostled near the sidelines. An irate de Guzman and his teammates seemed to suggest a Whitecap player had tried to stomp a Toronto player.
Vancouver's Le Toux was also ejected, for a second yellow card, for trying to take the free kick too early.
Wednesday's result means Toronto returns to the CONCACAF Champions League, a club cup tournament that covers North and Central America and the Caribbean.
Toronto FC made it to the semifinals of the CONCACAF tournament this year before losing to Mexico's Santos Laguna.
The CONCACAF winner (Mexico's Monterrey defended its title this year) advances to the FIFA Club World Cup, which features confederation club champions.
A poor opening 45 minutes saw Toronto attack but not take advantage.
Ecuador forward Joao Plata, who has not been much of a factor for Toronto in recent weeks, used his speed to rip into the Whitecaps defence. He came off to loud applause in the 78th minute.
Toronto looked like the team with the winning record in the first half. The home side moved the ball and found holes in the Vancouver defence. But it lacked the finishing blow.
The return of Toronto captain Torsten Frings, sidelined the last two games with a shoulder injury, was evident from the get-go. He found Plata with a glorious pass in the fourth minute and did it again minutes later with a cross that the five-foot-two sparkplug just managed to get a head to, sending it wide of goal.
Frings screamed for a penalty in the 19th minute when Plata went down in the box trying to chase down a cross from the left flank. But it looked like Plata had run into the defender.
There was a brief burst of offence from the Whitecaps. Fullback Alain Rochat's header was off the mark in the 22nd from a Camilo free kick. Then John Thorrington sent a shot over the bar.
But Vancouver struggled to get target man Hassli involved in the first half.
Frings, meanwhile, was yellow-carded in the 31st for a challenge that left Thorrington on the ground. The former German international pleaded innocence as his victim lay on the turf.
The Toronto captain hammered a free kick just wide in the 36th minute after Martin Bonjour was yellow-carded for bringing down Plata outside the box.
Vancouver's Le Toux was cautioned just before halftime for scything down fullback Ashtone Morgan.
Toronto came close in the 56th minute when Frings' deflected shot was just kept out by Cannon.
In last year's final, the two sides played to a 1-1 tie in Vancouver. The Whitecaps were up 1-0 in the second leg in Toronto, only to have the match called off due to torrential rain and lightning.
The match was replayed from 0-0 and Toronto won 2-1 to take the cup.
Toronto ousted the Montreal Impact and Vancouver defeated FC Edmonton to advance to this year's final.