Canon SX410 IS has a 20.0MP 1/2.3" (6.17 x 4.55 mm ) sized CCD sensor and features DIGIC 4+ processor. On the other hand, Canon SD780 IS has a 12.0MP 1/2.3" (6.17 x 4.55 mm ) sized CCD sensor . Canon SX410 IS's sensor provides 8MP more than Canon SD780 IS's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the SX410 IS and SD780 IS sensor size comparison.
Canon SX410 IS and Canon SD780 IS sensors have exactly the same size so none of them has any advantage over other in this area.