Question

to whom does wordsworth compare the solitary reaper. in brief

Answer 1

The poet compare solitary reaper as a lady who was cutting crops in field

Answer 2

He is comparing reapers song to the voice of Nightingale (cuckoo).
like Nightingale voice provide relief to the tired Traveller from their journey in desert in the same way the reaper girl had so hard impact on poet mind and soul.