Pentax X90 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Prime processor. On the other hand, Canon SX540 HS has a
20.0MP 1/2.3 (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 6 processor.
Canon SX540 HS's sensor provides 8MP more than Pentax X90'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 X90 and SX540 HS sensor size comparison.
Pentax X90 and Canon SX540 HS have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.