Size and weight are big decision factors when you are trying to find the ideal camera for your needs.
In this section, we are going to illustrate the Canon SX150 IS and Olympus E-P3 side-by-side from the front, back and top in their relative dimensions. Canon SX150 IS has external dimensions of 113 x 73 x 46 mm (4.45 x 2.87 x 1.81″) and weighs 306 g (0.67 lb / 10.79 oz) (including batteries). Olympus E-P3 has external dimensions of 122 x 69 x 34 mm (4.8 x 2.72 x 1.34″) and weighs 369 g (0.81 lb / 13.02 oz) (including batteries).
Below you can see the front-view size comparison of the Canon SX150 IS and the Olympus E-P3. Olympus E-P3 is 4mm shorter and 12mm thinner than Canon SX150 IS but it is also 9mm wider. As you can tell, actually this is not a fair size comparison since Canon SX150 IS has a built-in lens but Olympus E-P3 doesn't. Once you put a lens on E-P3, its thickness will increase significantly.
Now lets look at the top view comparison of Canon SX150 IS and Olympus E-P3.
Weight is another important factor, especially when deciding on a camera that you want to carry with you all day.
Canon SX150 IS is significantly lighter (63g ) than the Olympus E-P3 which may become a big advantage especially on long walking trips.
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-P3, the total kit will weigh much higher.
Weather Sealing
Unfortunately neither the Canon PowerShot SX150 IS nor Olympus PEN E-P3 provides any type of weather sealing in their bodies, 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 SX150 IS and Olympus E-P3's LCD screens have the same diagonal size of 3.00 inches.
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.