Cancelled first part of exercise, as this route much harder (3,5)
I believe the answer is:
off piste
'route much harder' is the definition.
I know nothing about this answer so I can't tell whether this works.
'cancelled first part of exercise as' is the wordplay.
'cancelled' becomes 'off' (similar in meaning).
'first' becomes 'ist' (ist resembles pst).
'part of' indicates putting letters inside (part of the inside).
'exercise as' becomes 'pe' (Physical Education. I am not sure about the 'as' bit.).
'ist' inserted within 'pe' is 'piste'.
'off'+'piste'='OFF-PISTE'
'this' acts as a link.
Can you help me to learn more?
(Other definitions for off piste that I've seen before include "away from regular paths" , "taking advanced course" , "moving away from regular ski runs" , "not keeping to established tracks?" , "Unconventional" .)