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 SX20 IS and Canon 1100D side-by-side from the front, back and top in their relative dimensions. Canon SX20 IS has external dimensions of 128 x 88 x 87 mm (5.04 x 3.46 x 3.43″) and weighs 600 g (1.32 lb / 21.16 oz) (including batteries). Canon 1100D has external dimensions of 130 x 100 x 78 mm (5.12 x 3.94 x 3.07″) and weighs 495 g (1.09 lb / 17.46 oz) (including batteries).
Below you can see the front view size comparison of Canon SX20 IS and Canon 1100D. Canon SX20 IS is 2mm narrower and 12mm shorter than Canon 1100D but it is also 9mm thicker. As you can tell, actually this is not a fair size comparison since Canon SX20 IS has a built-in lens but Canon 1100D doesn't. Once you put a lens on 1100D, 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 1100D is significantly lighter (105g ) than the Canon SX20 IS 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 1100D, the total kit will weigh much higher.
Unfortunately neither Canon PowerShot SX20 IS nor Canon EOS 1100D (EOS Rebel T3 / EOS Kiss X50) 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 Bridge Cameras with Weather Sealing Top DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Canon 1100D's 2.7" LCD screen is slightly larger than Canon SX20 IS's 2.5" screen.
On the other hand, Canon SX20 IS sports a Fully Articulated screen
which you can change the angle and position of the screen almost freely, making it possible to shoot from waist or over the head levels, and especially very useful for shooting selfies and video. On the other hand, Canon 1100D has a fixed type screen which provides almost no flexibility in shooting positions compared to SX20 IS.