Unless you know the type of the dictionary - and that means key and value - the only way to do it is to cast it to a Dictionary<object, object> - which is a very bad idea as it gets rid of the strong typing which makes C# so robust. At this point you are relying on runtime-casts to use the dictionary you create, and that's a poor idea.
Have you instead considered using Generics, so you don't have to cast your Dictionary, the types are inferred when you call the method?
void SomeMethod<K, V>(Dictionary<K, V> dict)
{
}
It'll make your code both more robust, and a lot easier to read.