Sure to be particular (7)
I believe the answer is:
certain
I believe this clue is a double definition.
'sure' is the first definition.
(similar in meaning)
'be particular' is the second definition.
(I've seen this before)
'to' acts as a link.
(Other definitions for certain that I've seen before include "Decided" , "Unquestionable" , "Absolutely sure" , "Sure, definite" , "Proved beyond doubt" .)