Why were some of the reasons French people (from Canada) didn't want confederation?

Actually, at the time Quebec was one province together with Ontario, so joining the Confederation would actually increase their rights to their own language and culture.

Their fears were rather that the central government would have too much power and if ever a conflict between the province and the Government shall arise, the province would loose

Some of the reasons why French people in Canada did not want Confederation because they believed that they might lose their rights and language. They believed that if Confederation occurred, a central government will cause the powers of the provinces to be weakened.