First thoughts -
I've taken his first name with a 'pinch of salt' - my lot used to use different names occasionally
Nearest I've come up with so far in Dumfriesshire , with father James is from BIVRI 2nd Edition:
Archbald Buhannan, bpt. 1818, Dryfesdale, Dumfries, Parents - James Buhannan and N Ladlaw
and a brother -
Benjamin Bell Buchanan, bpt. 1822, Dryfesdale, Dumfries, Parents - James Buchanan and Helen Laidle
I would think this is the same family - poorly transcribed - Helen Laidlaw probably

Not very good matches but I'm still looking!
Another possible is that he might have been illegitimate and that's a whole can of worms but his father would usually have been mentioned.
Again, there was quite a lot of secession from the established church and he could have been baptised outwith this.
Gadget