Sony WX350 has a
18.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor . On the other hand, Canon A1100 IS has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4 processor.
Sony WX350's sensor provides 6MP more than Canon A1100 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 WX350 and A1100 IS sensor size comparison.
Sony WX350 and Canon A1100 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 Canon A1100 IS has 49% larger pixel area (2.34µm2 vs 1.56µm2) compared to Sony WX350, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.