The Attorneys on this website only practice US Law. You need to consult with a French immigration Attorney.
The fact that you live illegally in France, without anything else, will not affect your ability to move to the United States, unless you are inadmissible for other reasons, such as having criminal convictions or prior violations of US immigration law.
I would recommend that you are an attorney to handle your case.
If the two of you marry your wife can sponsor you to immigrate to the USA. This is a process that takes at least 4 to 6 months and requires that a family petition be filed on your behalf and that you file an applucation to adjust status. I suggest that you and your fiance work with an experienced immigration attorney in the USA to complete the process. Everything can be done by mail, email, skype and fax.
Attorneys on Avvo practice US law. They cannot advise you on the laws and requirements of other countries.
You need to contact an attorney in the country in question.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.