Both Canon G16 and FujiFilm Z800EXR have 12.0 MP resolution sensors but Canon G16's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and FujiFilm Z800EXR's sensor is 1/2-inch (6.4 x 4.8 mm ).
Since Canon G16's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to FujiFilm Z800EXR.
Below you can see the G16 and Z800EXR sensor size comparison.
As seen above, Canon G16 has a 1.4x Larger sensor area than FujiFilm Z800EXR. 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.