There seems to be remarkably few French-language scientific extension blogs. Here are some good French sites:
1) Futura Science: https://www.futura-sciences.com/
French Site created in 2001. Has more than 3 million visitors per month. According to SimilarWeb, it is the 9th most frequented scientific site and the 241st most frequented site in France. This is not strictly speaking a personal blog, but it is a high quality site.
2) It goes up there: http://www.ca-se-passe-la-haut.fr
Eric Simon's personal website (Blog and Podcast) on astrophysics and the sciences of the universe. Very nice discovery. It's worth a visit
3) Amazing Science: https://sciencetonnante.wordpress.com/
David Louapre's Blog focuses on physics, but also on mathematics, chemistry, biology and the humanities.
4) Jpcmanson: https://jpcmanson.wordpress.com/
JP Manson's Blog on philosophy and epistemology.
5) Science Press Agency: http://www.sciencepresse.qc.ca/
The Science-Presse agency is a non-profit news agency founded in 1978. It is the only scientific news agency in Canada. The website is visited by almost a million visitors each year. The site contains a section with close to 100 blogs of Quebec scientists or organizations.