In Switzerland, they are not put up in tins
I believe the answer is:
cantons
'in switzerland they' is the definition.
The definition suggests a plural noun which matches the answer.
'not put up in tins' is the wordplay.
'put up' shows that the letters should be reversed in order.
'in' indicates putting letters inside.
'tins' becomes 'cans' ('can' can be a synonym of 'tin').
'not' backwards is 'ton'.
'ton' put inside 'cans' is 'CANTONS'.
'are' acts as a link.
Can you help me to learn more?
(Other definitions for cantons that I've seen before include "Territories" , "Swiss administrative divisions" .)