They are only interchangeable in the definition 2 here, not otherwise:
http://www.m-w.com/dictionary/choice
See the Synonyms section.
This corresponds to being interchangeble when talking about a selection:
In selecting a book at the bookstore, I had many options or choices.
I had many options or choices in terms of payment (cash, cards, etc).
but not otherwise:
Many examples are to be found here:
http://www.answers.com/topic/choice
http://www.answers.com/topic/option
I'd suggest to study them. They are very good.