I think that only situation where it would sound OK to use the preposition 'in' to connect 'opinion' and the subject in question would be a fairly general topic with a plural noun. You might possibly say "I have no opinion in these matters", where 'in' suggests 'amongst'.
Otherwise, these are your main options:
with regard to
in regard to
(Note that 'in regards to' and 'with regards to' are not considered correct. They are very common native-speaker errors).