^
Because japanese doesen't diffrenciate between the two sounds, they can use sounds similar to both ends of the spectrum for effect (like in the link below where in the intro there are clearly rollied rs like standard pronunciation of the letter R in most of the continental languages that aren't using the french R). In languages that give this phonetical difference some value this would be considered faulty and children with this problem given tutoring to learn correct pronounciation.
morning musume shabondama
Rody! I think it's a very interesting subject too.
As for the final nasal sound in Marron, depeding on the speaker it can be pronounced clearly, omitted, slightly nasalize the preceding vowel (turning the japanese pronounciation of the last syllable in marron into something very similar to the french pronounciation of the same syllable) or in some cases even a slight ng sound.