Canon 750D has a 24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features DIGIC 6 processor. On the other hand, Canon 700D has a 18.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 5 processor. Canon 750D's sensor provides 6MP more than Canon 700D'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 750D and 700D sensor size comparison.
Canon 750D and Canon 700D sensors have exactly the same size so none of them has any advantage over other in this area.