This story was first reported at MercatorNet, and claims that

The proportion of Christians in the country – which currently stands at about 34 percent — is slowly increasing. By 2030, it will rise to 37 percent and by 2045 to more than 39 percent. And because hundreds of thousands of overseas Lebanese are eligible to vote, the increase in registered voters is even more impressive. By 2030, 40 percent of Lebanese on the electoral roll will be Christian, and by 2045, the figure will be 41 percent.

But taking a census is just not done in Lebanon as it is two politically touchy. Sunni and Shiite Islamic factions share power with the Christian population. An interesting article about a very complex situation.