Balloonist set out a route across North America (8)
I believe the answer is:
aeronaut
'balloonist' is the definition.
(I've seen this before)
'set out a route across north america' is the wordplay.
'set out' indicates anagramming the letters.
'across' is an insertion indicator.
'north america' becomes 'na'.
'a'+'route'='aroute'
'aroute' anagrammed gives 'aerout'.
'aerout' enclosing 'na' is 'AERONAUT'.
(Other definitions for aeronaut that I've seen before include "Pilot, flier" , "Early traveller by air" , "Balloonist" , "Pilot - Eton aura (anag)" , "Space pilot" .)