A couple of observations...
Will by its very nature involves the ability to make choices. Thus "free-will" is almost a redundancy.
Will is the ability to intend or desire something, and/or the ability to act upon a choice or an intention.
Without the ability to make a choice, or to desire, will is essentially meaningless. It doesn't exist.
While this doesn't prove that will must always be unconstrained, it does suggest that "free-will" is the natural state of any will, and that constrained will is an unnatural, imperfect state.
Now, we clearly have the appearance that we have will. This is something that virtually every sane person would take to be self-evident. We undeniably make decisions, we undeniably have desires and intentions, we undeniably act upon decisions.
It would seem, therefore, to be undeniable that we have will. If we accept this, it would suggest that we are, by nature, creatures of will, and therefore since will by nature is free, we are by nature creatures of free will.
The question that some ask is essentially this... is our will, or our "free-will" an illusion?
One of the basic premises of this question is the idea that constraints, or limits, upon the will can prove will to be "not free", but rather determined by outside factors.
In my opinion there is a problem with this reasoning. Limits, or even constraints upon the will do not necessarily deny the ability to make choices or to have desires etc.
In essence the argument is something like this.. since outside factors restrain me from making any choice I want, I therefore have no choice.
My response is that even if your choices are limited or restrained by outside factors, you still have choice.
In other words, limited choice is not no choice.
So for example, what some of the arguments amount to is that because the law of gravity prevents me from simply choosing to fly through the air, or because physics and biology prevent me from breathing water, I can't choose to breath water... therefor I do not have free-will.
It is undeniable that there are limits on our ability to choose. However, those limits do not prove that we have no choice. In fact, quite the opposite. The very fact that there are limits suggests that within those limits choice exists.
Another common argument is that deterministic chains of cause and effect essentially over-rule free will. Our choices are all predetermined by factors that we do not choose. Therefore we have no real choice and no free-will.
The first problem with this is that it is just as impossible to prove this as it is to prove the converse. At best you have two options that can be reasonably argued and you must choose which one you believe.... which is rather ironic.
It is possible that my decisions could all be determined by my genetics, and a combination of outside factors such as weather and what not. But no one could ever prove this. You can choose to believe it if you like.
Now, one example that is used in this kind of argument is that of personal tastes. It is asserted that we do not choose our tastes, things we enjoy and things we don't enjoy... we discover them and they seem to be determined by possibly genetics, possibly environmental factors, possibly some combination of the two.
This same basic principle can be applied to any human behavior, and indeed it is in the field of psychology.
Yet, we know that though tastes and behaviors often seem to be determined by outside factors, we can change them by our own choices.
A person may not like coffee, but if they decide to like coffee they can drink it until they develop a taste for it.
Behaviors can also be modified based on similar principles.
This, in my opinion, suggests that though there are constraints and limits, we are free to make choices not only within the limits but even which attempt to change the limits and change the constraints.