Keanu Reeves and Carrie-Anne Moss were casted together because they have the same eyes.
It's not just their eyes themselves, it's the look in their eyes (worried I guess), it's the same in the entire trilogy !
shareExcept that they don't have the same eyes, Reeves has dark brown eyes and Moss has blue eyes.
Other than that, yes, they could be siblings! There's a bit of physical resemblance with their height and coloring, and yes. The attitude and body language. And black wardrobes...