Both Nikon D3400 and Canon T8i have APS-C sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another difference between these two cameras is that Nikon D3400'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 D3400 and T8i sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D3400 and Canon T8i Cameras
As seen above, Nikon D3400 has a 1.1x Larger sensor area than Canon T8i. 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.
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
Nikon D3400
or the
Canon T8i ,
including hyperfocal distance.
