Olympus SP-810 UZ has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features TruePic III+ processor. On the other hand, Canon SX410 IS has a
20.0MP 1/2.3 (6.17 x 4.55 mm ) sized CCD sensor and features DIGIC 4+ processor.
Canon SX410 IS's sensor provides 6MP more than Olympus SP-810 UZ'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 SP-810 UZ and SX410 IS sensor size comparison.
Olympus SP-810 UZ and Canon SX410 IS have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Olympus SP-810 UZ has 44% larger pixel area compared to Canon SX410 IS, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.