The Skrill Conference Premier League side ran away with the game in the second period after Gosport, who are struggling near the bottom of Conference South, gave them plenty of trouble early on.
Borough were denied an early goal by Cambridge keeper Will Norris, who made a fine save from a Justin Bennett header.
Portsmouth loanee Ryan Bird wasted a chance for the U's before Bennett fired over the bar on another Gosport raid forward.
But it was Bird who opened the scoring, vitally just before half-time, when he beat the offside trap to run on to a ball from Luke Berry and lob advancing Gosport keeper Nathan Ashmore.
Cambridge continued that momentum into the second 45 minutes and were 2-0 up on 50 when Ryan Donaldson sprinted on to Tom Champion's through-ball and rounded Ashmore before passing into an empty net.
The game was over as a contest on the hour when Donaldson scored his second, reacting quickest to rifle the ball past Ashmore after a Cambridge shot hit the post and caused an almighty scramble in the box.
Bennett dragged a shot wide on a rare Gosport attack but Cambridge grabbed their fourth 12 minutes from time when Berry scored from the penalty spot after Andy Pugh was felled by Sam Pearce.
Borough sub Dan Woodward hit the bar in the closing minutes but there was to be no consolation goal for his side and it was Cambridge who lifted the trophy - they now turn their attentions to their bid for promotion, most likely via the playoffs.