I use to tow a SeaDoo jet ski with a 2007 Ford Focus Zetec 2.0L, it pulled it just fine even with the A/C on, but I think the Polo will pull it better because its not as heavy as the Focus.

Just a thing to watch out for, dont unload/load your jetski on a ramp that has sand on it, with the thin tyres the Polo has, you'll have grip issues getting it up the ramp especially with the low end torque.