Fujifilm X-T20 has a
24.0MP APS-C (23.6 x 15.6 mm ) sized CMOS X-TRANS III sensor and features X-Processor Pro2 processor. On the other hand, Canon SX420 IS has a
20.0MP 1/2.3 (6.17 x 4.55 mm ) sized CCD sensor and features DIGIC 4+ processor.
Another difference between these two cameras is that Fujifilm X-T20's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the X-T20 and SX420 IS sensor size comparison.
As seen above, Fujifilm X-T20 has a 13.1x Larger sensor area than Canon SX420 IS. 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.