Here's a rough overview of what it would take to get to where you can practice in ObGyn or family med plus obstetrics in the US, after doing some or all of your ObGyn residency in France.
1. Register with ECFMG and get certified. Usually this means getting transcripts evaluated and taking an English proficiency exam. ecfmg.org
2. Take the 3 US board exams (USMLE 1,2,3). 2 & 3 have parts that have to be taken in the US. Prep is difficult and expensive. Step 3 may be later in the process, but many foreign grads get it done early to add to credibility. nbme.org
3. Find US programs that will allow you to do observerships, such as inpatient medicine. This gets you recommendation letters and credibility.
http://www.ama-assn.org/ama/pub/education-careers/graduate-medical-education/freida-online.page?
4. Apply for residency in late summer. Many foreign grads apply to over 100 programs.
5. Go on residency interviews October - February.
6. Wait for the match in March. If you match, you are legally bound to take the spot. If you don't match, you can try to pick up an unfilled spot, or try again the next year. The match rate for foreign medical grads is currently 50% and falling. You can get more info on the match at nrmp.org.
7. Deal with citizenship and permanent residency paperwork. Learn how to live in the US etc.
The above is what you have to do before 4 years of residency. If you can work full time on these objectives, earning nothing and spending a great deal, then it could theoretically be done in 2 years.
Of note, the US is enormous and fragmented. You can't assume you'll have any control over where you end up for residency.
Hope that helps. Basically your husband is asking you to redo your training, have no income for 2+ years, and then have a minimum wage job with an 80 hour work week for 4 years.
If you do not yet have any experience with US healthcare, I suggest getting some exposure as a
first step. You will almost certainly find it barbaric. You may have heard of Obamacare: 50% of the US thinks Obamacare is bad because it's
not socialized medicine, and the other 50% thinks Obamacare is bad because it
is socialized medicine.
Best of luck to you.