I've gathered information about a few Polish Saints here.
All these saints lived/worked in Poland but none of them was an ethnic Pole. The only saint (1) whose ethnicity was Polish*, (2) who lived and died in communion with the Orthodox Church, (3) who was officially glorified by the Orthodox Church, and (4) who is listed as a saint by a contemporary Orthodox source approved by an Orthodox bishop, seems to be St Christian. Sts Matthew and Isaac, his companions in martyrdom, probably also meet these requirements (probably, because sources describe them as being "of Slavic country and tongue" but do not specify which
* including the earliest stages of the formation of what we know today as Polish ethnicity
** tongue did not need specification as in the 11th century, it was more or less the same among all the Slavs