Nikon P300 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Expeed C2 processor. On the other hand, Canon SX600 HS has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 4+ processor.
Below you can see the P300 and SX600 HS sensor size comparison.
Nikon P300 and Canon SX600 HS have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Nikon P300 has 32% larger pixel area compared to Canon SX600 HS, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.