1.e4 c5  2.c3 d5  3.e5?! Bf5!  4.d4 e6 transposes to either the Advanced French with the bishop outside the pawnchain or the Caro-Kann with an extra tempo.  Therefore white must play 3.exd5 but I know that has nothing to do with 3.b3!

3.b3 is not so bad after 2...e6, as Black's best lines against the b3 set-up generally involve ...e5, which now comes at a loss of tempo.  However, it is still a bit of a 'sideline', and Black should be OK.

After 3.c3 d5 you are not obliged to play 4.e5 and transpose to the French - it is perfectly legitimate to play 4.exd5 when White can still hope to play for an advantage after either 4...Qxd5 (transposing to a 2.c3 d5 line) or 4...exd5, which is usually reached via a 2.c3 e6 move order.

Of course you also have to be prepared for 3...Nf6(!) ...