After some good pressure Canvey took a deserved lead when Chris Duffy scored on six minutes.
The right-back's hopeful cross into the box somehow looped over the stranded Shaun Marshall before dropping into the net.
After their emphatic start, the Gulls looked to build on their lead and Lee Boylan was unlucky when his shot from John Keeling's cross was well saved.
Boro failed to deal with the threat of Keeling and they were punished on 16 minutes when the winger's cross was headed in at the far post by Ollie Berquez.
The 2-0 deficit sparked a fight back from Boro and Dannie Bulman was unlucky to see his shot deflected and then well-saved by Danny Potter.
The keeper was again called upon when he saved well from Anthony Elding and Simon Weatherstone to send the home team in two goals up at the break.
After the restart Boro looked to claw themselves back into the game but their chances were dealt a massive blow when George Boyd received his marching orders from referee Martin Yerby.
Boyd's late challenge on Duffy warranted a straight red card.
Seven minutes later they were reduced to nine men when Weatherstone was shown a second yellow card for smashing the ball away after the referee had awarded a foul.
It was a harsh decision on Weatherstone who had been booked in the first minute for a foul.
Late substitute Junior McDougald completed Boro's misery when he added a thrird with five minutes to go.
Canvey Island are now unbeaten in five matches at home, while Boro have lost four of their last away fixtures.