Canon 1100D has a
12.0MP APS-C (22.2 x 14.8 mm ) sized CMOS sensor and features Digic 4 processor. On the other hand, Canon SL3 has a
24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features DIGIC 8 processor.
Canon SL3's sensor provides 12MP more than Canon 1100D'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 1100D and SL3 sensor size comparison.
Sensor Size and Resolution Comparison image of Canon 1100D and Canon SL3 Cameras
Canon 1100D and Canon SL3 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.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Canon 1100D
or the
Canon SL3 ,
including hyperfocal distance.