Well to be honest, if you're willing to become a transplant surgeon in France, then that's the only alternative you have --to study there.
If you want to work in the US, it's best that you look into American medical schools (and if that doesn't work, may be you could look into the top 4 Caribbean schools.)
Regarding French, you better be really good because it would pretty much not work if yo had only "passable" French skills. The concours is a nightmare. I have 5 French friends (3rd year students) doing an exchange program at my university and they told me that it was nothing but a nightmare (and they were French!) Appreantly only 200-400 out of 1000-1200 students make it through th concours into the 2nd year. You only get 2 attempts and if you miss it, then you're barred from studying in any medical school not only in France but also in Switzerland and Belgium.
Lastly, your future specialty depends on the ECN (Examen Commissant National) which and your rank on that exam determines your residency. As long as you have an EU degree, you won't have any problems getting your degree recognized. You will be treated the same...which means you have to compete with the rest of the French students for a specialty.
So how realistic is it? Depends on a lot of factors: your level of French comprehension, your performance on the exams (Concours, ECN etc.), your ability to study medicine in an entirely different language etc.
If you're serious about living in France, I'd recommend you take a year of French courses (some sort of a pre-medical preparation in Physics, Chemistry and Biology) and then get into a school. That will definitely make you better prepared.