You can transpose to Sicilian via Nf3 or c3, or play French Advance after c3 d5 e5. Or play d5 and get Franco-Benoni.
3.Nf3 Nc6 is kind of bad because of d5. Black should take on d4 first and only then play Nc6. Then you'll get Taimanov or Maroczy via 5.Nb5 d6 6.c4.
To tell you the truth, I don't face a lot of opening weaknesses when it comes to 1. e4. However, when my opponent plays a French and plays 2...c5, what should I do? Of course, it would be natural to transpose into a Sicilian with 3. Nf3, but what happens if my opponent plays 3...Nc6? (That question mark is for the sentence, not for the annotation.) I mean, I gain a tempo, but what move should I make?
Thanks!