できる is a tricky verb because it both means "to form / to be built / to be ready" and "to be able to [suru-verb] / to do [suru-verb] easily".
But when it's followed by やすい, できやすい means "tend to form ~", "tend to be built as ~", "easily turns into ~", etc, because やすい already means "easily / can / has a tendency to ~".
- フランス料理は作りやすい。: OK, (as a general fact) French cuisine is easy to prepare. A person who says this must be a very good cook.
フランス料理が作りやすい。: Exhaustive-listing が. (Among other cuisine in the world) It's French cuisine that one is good at.
フランス料理はできやすい。: ("French cuisine easily forms"(?) Makes no sense to me)
フランス料理ができやすい。: Something like "It easily produces / turns into French cuisine". It sounds like you were using a game item which gives 'French cuisine' or something different randomly.
フランス料理はできる。: Contrastive は. A person who said this is good at French cuisine, but implies he's not good at other types of cuisine.
- フランス料理ができる。: Neutral-description or exhaustive-listing が, depending on the context. A person who said this is good at French cuisine.