Size and weight is a big decision factor when you are trying to find the ideal camera for your needs.
In this section, We are going to illustrate Canon SX120 IS and Olympus E-PL3 side-by-side from the front, back and top in their relative dimensions. Canon SX120 IS has external dimensions of 111 x 71 x 45 mm (4.37 x 2.8 x 1.77″) and weighs 285 g (0.63 lb / 10.05 oz) (including batteries). Olympus E-PL3 has external dimensions of 110 x 64 x 37 mm (4.33 x 2.52 x 1.46″) and weighs 313 g (0.69 lb / 11.04 oz) (including batteries).
Below you can see the front view size comparison of Canon SX120 IS and Olympus E-PL3. Olympus E-PL3 is clearly the smaller of the two cameras. Its body is 1mm narrower, 7mm shorter and 8mm thinner than Canon SX120 IS. As you can tell, actually this is not a fair size comparison since Canon SX120 IS has a built-in lens but Olympus E-PL3 doesn't. Once you put a lens on E-PL3, its thickness will increase significantly.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Canon SX120 IS is 28g lighter than the Olympus E-PL3 but we don't think this will make a significant difference.
Again, this comparison may not be very useful in real life as we are comparing the weight of a camera with a built-in lens to the body-only weight of an interchangeable lens camera. Once you put a lens on E-PL3, the total kit will weigh much higher.
Unfortunately neither Canon PowerShot SX120 IS nor Olympus PEN E-PL3 provides any type of weather sealing in their body, so you have to give extra care especially when you are shooting outdoors. If weather sealing is a must-have feature for you, check these sections: Top Compact Cameras with Weather Sealing Top Mirrorless Cameras with Weather Sealing
LCD Screen Size and Features
Canon SX120 IS and Olympus E-PL3's LCD screens has the same diagonal size of 3".
On the other hand, Olympus E-PL3 features a Tilting screen
where you can change the angle of the screen to make it easier to shoot from waist or over the head levels whereas the Canon SX120 IS has a fixed type screen which provides less flexibility in shooting positions compared to E-PL3.