Some cameras are weather-sealed and some aren't. In the Canon lineup, only their top cameras are designated "weather-sealed", but cameras lower in the lineup have some weather sealing. Bottom line -- they'll give you some protection, but you test it at your own risk. You should also know that weather sealing depends on the lens, including, in some cases, a UV protector or other front-element protection.
In practice, I'm not too concerned about the occasional sprinkle, but if I were actually going to shoot in the rain, I'd want something resembling actual weather protection for my kit.