"Can you..." and "Will you..." are the same, aren't they? Not really. "Can" is associated with capability, while "will" is associated with a choice. Using the right word in the correct situation may mean the difference between harmony and defensiveness. When do you use one over the other?
Many times we tend to start a request with "Can you..." For example, "Can you drive me to the store?", "Can you take out the trash?" While asking in this way seems normal to us, it may actually put someone on the defensive. What you are actually saying is, "Are you competent enough to drive me to the store?", "Are you capable of taking out the trash?" Doubting someone's abilities may put them on the defensive, making them averse to saying "yes".
Using "will", as in "Will you drive me to the store?" or "Will you take out the trash?", implies the person is capable and you are giving her/him the choice. Most people, when presented with a choice, like to help -- they will usually respond with a "yes" versus a "no". When you do hear the occasional "no", accept it gracefully.