I saw a nearly jet black squirrel in ardeche today, carolinensis have invaded the UK and Italy, however I didn't find news about their arrival in France. Was that black squirrel really a Canadian species?
Yes, Sciurus carolinensis has been invasive in France, Italy and Switzerland for quite a few years already (Bertonlino and Genovesi, 2003).
Note that the "original" distribution of S. carolinensis is over eatern Canada and USA. Not Canada only.