USA, Canada /
Canadian wanting Polish Citizenship? [30]
If only one of your parents is Polish born in Poland - you are also a Polish citizen
If only one parent is a Polish citizen then the child's citizenship is not necessarily automatic. That is actually the parents' decision which citizenship the child will have. A child in this situation may, however, apply for the Polish citizenship if he/she is between 16 and 17 years and six months of age. After that, it is all an individual case. Persons whose only one parent has Polish citizenship are treated favorably in respect to their Polish citizenship applications.
Note: don't treat the above as legal advice. Call Polish consulate/embassy to make sure all the details are clear.
How easy is it to obtain a Polish passport if your grandparents were Polish born (parents were Canadian born)?
There is a "citizenship continuity" principle in the Polish law. That means that: if your grandparents (from both the mother and the father side) were Polish born then their children are automatically Polish citizens. If this applies to your situation then you are a Polish citizen.