Any shotgun can be an effective turkey gun. In Ontario, the regulations require you use a minimum 20ga. with only #4,5,6 or 7 shot sizes permitted. Typically, a full or extra full/turkey choke is used, with heavy 3" or 3 1/2" loads of lead or, increasingly, non-toxic shot (tungsten, Hevi-shot, etc.). But, that is not required - we've killed several turkeys with a modified choke 20ga. with 2 3/4" loads and I've shot more than a dozen with a straight cylinder bore 20ga. flintlock and 1 1/8oz. of #6's.
So, any 20ga or larger with a choke of about modified or tighter will serve just fine. Shorter barrels are generally handier and pattern just as well as longer barrels, so if you're buying a gun specifically for turkeys I'd look at a 12ga. or 20ga. with a barrel of 21"-26", threaded for choke tubes and with a 3" chamber (or 3 1/2" if you really want). Turkey hunting should be a one shot game, but I'd recommend a pump or semi for a new hunter. Rem 870, Benelli Nova, Browning BPS, Mossberg 500/835, Winchester SXP, etc. - me are certainly better quality than others, but it doesn't really matter much for a 2 shot hunting season. Camo guns are nice, but not necessary. If you're a waterfowl hunter, you likely already own a gun that would serve well for turkeys.
For chokes and ammo, don't get too crazy or overthink it. A full choke with a quality 3" lead #5 or 6 load (I'm not a fan of 4's) will typically be plenty of medicine out to 30-35 yards or a bit more (it's a very good idea to pattern a couple different loads and confirm your effective range). I've seen more people miss turkeys by being over choked - they buy super extra full, construction specific name brand fancy packaging turkey chokes and spend way too much time trying to find a choke/ammo that will kill a turkey at 50++ yards. Then they have a gobbler come in properly and they miss at 15 yards because they have a pattern the size of a softball and the adrenaline has made them half blind so they forgot to aim small (or in some cases, they did aim but never patterned their gun at close range so didn't know it shoots high or left/right really close). I could go on forever about chokes and patterns for turkeys.
You'll likely find the biggest problem of turkey hunting is securing a property to hunt that has turkeys, not having to share it with other hunters (or trespassers) and then figuring out how it's done. The details of your gun are fun to think about, but as long as you're in the general ballpark as described, you're set to hunt.
