Ravi Zacharias sort of assumes (but I don't think ever tries to prove) that God is sovereign, and in that sovereignty has decided to give us wills of our own.
To begin the chapter "Does Prayer Make Any Difference?" in Zacharias' book Has Christianity Failed You? Zacharias states that
Christianity does not promise that you will have every question fully answered to your satisfaction before you die, but the answers it gives are consistently consistent. There may be paradoxes within Christian teaching and belief, but they are not irreconcilable.
Though he is speaking from the context of sorrow and unanswered prayer he does touch a bit on how our wills related to God's in prayer:
Through Jesus' prayer in Gethsemane we learn the most important thing about prayer -- that it is ultimately a conversational relationship in which God does for you what you cannot do for yourself. It is not trying to persuade God to rethink his will but the means through which God reshapes you into a person who desires his will and is content to receive it, regardless of what it entails.
This is not fatalism. It is not defeat. It is not confusion. It is not a cop-out. It is sometimes easier to resist God's will than to have faith and confidence in God and in his specific purpose for each one of us.
In The Grand Weaver (excerpt here), he retells a story written by Arnold Fine, of high school sweethearts, separated by a parent, that re-meet in their old age. The story ends with "How good the work of the Lord is", but Zacharias notes that there are three wills in play in addition to God's; "the work of a sovereign God leaves all of us overwhelmed at the way God weaves the threads."
Zacharias makes no attempt to fit the free will vs. determinism argument into a logical framework that makes perfect sense and fits in a shiny box1 -- in whatever way God may work in and through people, he does it in a way that does not override their freedom. In his book Walking from East to West, he says that God works "from the shadows", nudging, pushing, and guiding, rather than forcing and dominating.
1 Like many apologists, Zacharias tends to avoid internal theological debates, preferring to focus on presenting or defending the common beliefs of [a subset of] Christianity.