I'd guess Belgian but only because most "French-style" guns are Belgian made. They are difficult to date from pictures because they were being made right up to the beginning of the 20th century albeit for the African/North African market... places where the colonial governments would not allow the local people to have more modern arms. A look at the proof marks would be essential - they will at least tell where the barrels were made and, if Belgian as they probably are, can at least identify a very late date. The wide rounded tail end of the lockplates, more like a percussion lock than a flint lock also suggest a fairly late date. Quality is also an issue... it tended to decline over time but I suspect that fairly good quality examples can also be quite late even though they are much more rare than low quality examples.
