Below you can see the front view size comparison of Canon 77D and Canon 90D. Canon 77D is clearly the smaller of the two cameras. Its body is 10mm narrower, 5mm shorter and 1mm thinner than Canon 90D.
Canon 77D vs Canon 90D - Front View
Canon 77D vs Canon 90D - Top View
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.
Camera Size Comparison
Select Two Cameras for Size Comparison