Canon T7 has a 24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 4+ processor. On the other hand, Sony A57 has a 16.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor .
Canon T7's sensor provides 8MP more than Sony A57'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 T7 and A57 sensor size comparison.
As seen above, Sony A57 has a 1.1x Larger sensor area than Canon T7. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Canon T7 and Sony A57 sensors have been tested by DxO and the results show that A57 has a better overall score of 75, 4 points higher compared to T7's score of 71.