Below you can see the front view size comparison of Canon 80D and Pentax K-3. Pentax K-3 is clearly the smaller of the two cameras. Its body is 8mm narrower, 5mm shorter and 2mm thinner than Canon 80D.
Canon 80D vs Pentax K-3 - Front View
Canon 80D vs Pentax K-3 - 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