A two-against-three is sometimes called a "hemiola." (Next time you see it in a trivia game, you'll know.)
You can always work out polyrhythms by taking the least common multiple of the two voices, and working out where the notes hit. So, with two against three, the LCM is six. Count in sixes. Both voices hit on one, the three hits on 3 and 5, and the two ...
Yes, you could call this 'two against three' pattern a simple example of Polyrhythm. Not sure why it's so important to label it? More importantly, have you a strategy for PLAYING it?
The count is 1 2-and 3.
The 3-group hits 1 2 3.
The 2-group hits One and.
Practice it tapping two hands on the table before trying to play it.