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 400D and Leica Digilux 3 side-by-side from the front, back and top in their relative dimensions. Canon 400D has external dimensions of 127 x 94 x 65 mm (5 x 3.7 x 2.56″) and weighs 556 g (1.23 lb / 19.61 oz) (including batteries). Leica Digilux 3 has external dimensions of 146 x 87 x 77 mm (5.75 x 3.43 x 3.03″) and weighs 606 g (1.34 lb / 21.38 oz) (including batteries).
Below you can see the front view size comparison of Canon 400D and Leica Digilux 3. Canon 400D is 19mm narrower and 12mm thinner than Leica Digilux 3 but it is also 7mm taller.
Now lets look at the top view comparison of Canon 400D and Leica Digilux 3.
Weight is another important factor especially when deciding on a camera that you want to carry with you all day.
Canon 400D is 50g lighter than the Leica Digilux 3 but we don't think this will make a significant difference.
Also keep in mind that body weight is not the only deciding factor when comparing two interchangeable camera bodies, you have to also take into account the lenses that you will be using with these bodies. Since Canon 400D has an APS-C sized sensor and Leica Digilux 3 has a smaller Four Thirds sensor, Leica Digilux 3's lenses for a similar focal length and aperture will generally be lighter and smaller than the Canon 400D lenses.
Unfortunately neither Canon EOS 400D (EOS Digital Rebel XTi / EOS Kiss Digital X) nor Leica Digilux 3 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 DSLR Cameras with Weather Sealing
LCD Screen Size and Features
Canon 400D and Leica Digilux 3's LCD screens has the same diagonal size of 2.5".
Unfortunately, both cameras has fixed screens so they don't tilt or flip in directions.