Substitute for rooster

You can of course use a chicken. While you won't know if it is a hen or a rooster, it should perform fine in the dish.

As a braised dish, you may do well with an older bird, although these are hard to find in the modern shopping environment. You might use a roaster (which will be quite large, but older), or a stewing hen if you can get special order one.

Taking Daniel Chui's comment about this being similar to Coq au Vin, you could take the recommendation from Good Eats, and use a stewing hen, or if you can't find that, use all dark meat (4 thighs + 4 legs)

AB: Now, why would a classic dish like coq au vin call for a tough old rooster? Because, the average 17th century French country housewife had roosters, okay? And when one of them was no longer capable of performing its rooster-ly duties, she needed a dish to justify doing away with the old guy, right? Now, such a dish would certainly take advantage of the rooster’s fully developed physiology, right? Including a considerable amount of connective tissue. Now, take a look around the poultry case at your local market, and odds are, you’re not going to find any rooster.

AB: [to butcher] Rooster?

BUTCHER: [shakes his head]

Didn’t think so. Okay, the next best thing would be a stewing hen. Stewing hen is a chicken that is usually about a year of age, it’s kind of retired from laying eggs, so they’re pretty tough.

AB: Stewing hens?

B: [shakes his head]

AB: Some specialty markets carry them, but truth is, most Americans like their chicken young, tender, and relatively flavorless, so what sells are broiler fryers and roasters. Now broilers are typically harvested around twelve weeks of age, and roasters aren’t much older. Of course, neither comes close to giving us the kind of flavor or texture that we would get from a stewing bird or a rooster. So, for this dish, we’re gonna go with the next best thing. Thighs and legs.

AB: Thighs and legs. Four of each, please.

B: [nods, goes to fill the order]

AB: They don’t have a lot of age on them, granted, but they’ve got more connective tissue and flavor than anything else in this case.

I'm pretty sure most, if not all chickens sold commercially are hens unless otherwise specified. I think the best bet is to ask a butcher for a rooster/capon (which I'm sure they could get for you). Barring that, I would go with a free range/organic chicken instead of a broiler/fryer hen which has no taste and probably won't work well (sounds like this is a version of coq au vin). Alternatively, you could use a stewing hen in the stock (very flavourful, lots of collagen etc) and then cook a separate broiler/fryer separately and add the meat to the dish after. The stewing hen would be too chewy to eat.

The major difference between hen and a rooster meat is that rooster tends to have less fat and more protein (i.e., it's meatier). Hence, store-bought "chicken" can be either-or.

Braising is a preferred method of cooking "tough"/lean cuts of meat, so Rooster is marginally better in this preparation, but not by much.

Honestly, I'd just ask your local butcher. Depending on where/how he gets his meat/animals, he might know whether he's selling you a hen or rooster.