The club's all-time leading goalscorer, who signed a contract extension this week that will keep him at the club until 2021, opened the scoring after 32 minutes.
So often the star of the show, Aguero shared the spotlight on a rainy afternoon in South Wales with Bernardo Silva, who doubled City's lead three minutes later, and Ilkay Gundogan, who capped a fine performance with a brilliant solo effort.
Substitute Riyad Mahrez scored his first goals for the club with a brace to put the result beyond doubt, and the manner of the victory will have delighted Guardiola after a below-par showing in a 2-1 defeat to Lyon in midweek.
Cool and composed during a scrappy opening half an hour, Gundogan started the move that led to the opener, feeding Silva who squared to Aguero and the striker beat his marker to apply a first-time finish.
Silva got his head underneath Leroy Sane's cross from the right two minutes later and looped the ball up and over Cardiff goalkeeper Neil Etheridge and in at the far post.
Gundogan was the stand-out player in the first half and he was rewarded with the pick of the goals, playing a one-two with Raheem Sterling before confidently side-footing into the top corner.
City controlled the second half from start to finish and when Sterling set Gundogan free down the left, he sent a low cross to the feet of Mahrez to open his account for the club.
With one minute left to play, Bruno Ecuele Manga needed to make a simple clearance, but instead played the ball straight to Mahrez, who drove it low and hard into the bottom-left corner of the net to wrap up a thoroughly enjoyable afternoon for Guardiola.
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