There is a cedar on the country flag.

The ancient world knew Lebanon as a region rich in high-quality cedar. Vestiges of that legacy can be traced back very far.

For French, the closest reference to hand is probably its frequent reference in the Bible.

The two concepts have been explicitly linked in French since at least the Revolution.

However, it appears that the exact collocation pays du cèdre is only a few decades old in Ngram data.

I like qoba’s theory below about pays du cèdre coming into popular use during the Lebanese civil war in order to vary journalistic style.