Saying nasal vowels when you're speaking English is silly. The word Saison has been used enough to be considered an English word of French origin. Don't use phonemes that don't exist in the middle of an English sentence unless you want to sound pretentious.
Actually, if you want to get all technical here, nasal vowels are used in American English, appearing before nasal consonants, in words like "man," "can't" and "then," and "embalm." In British English they're not all nasalized, noticeably "can't." You probably don't notice how they're nasalized because you're a native American English speaker.
If you've ever heard someone who uses African American vernacular English, or some related southern accents say "Hey man" you've definitely heard a nasal "n."