Quoted:
I was looking at getting a 20 guage with the cantilever rifled barrel but didn't know a whole lot about it (the cantilever barrel). You can mount a scope to that rail that's attached? What rings can withstand the recoil?
That would be an excellent choice.
With rifled slug barrels used on pumps you want the scope mounted on the barrel, not the receiver. Cantilever was developed as a way to accomplish that and also allow the use of scopes with shorter eye relief. Before that the mount was forward on the barrel and you had to use handgun scopes. Now you just mount up with pretty much the same rig you would use on a larger caliber rifle. There are plenty of scopes made for shotguns, just do your homework and you will see them offered by every major brand. 1x5, 2x7 or a 3x9 will do fine but if you are not sure, lower powers are better for closer shooting.
I have used rifled barrels for over 27 years now and I usually use a red dot, 1.5x or 2x fixed power. I have stayed at 100 yards and in for shots, old habits die hard. One of these days I will put a variable power scope on, but I suggest you use one.
20 gauge is a great choice, a little lighter gun carries easy, add a vent rib barrel for a good all around gun. The newer sabot rounds are pretty hot. You are basically shooting a short range .50 cal.
There are packaged guns out there that come with both a rifled barrel and smooth bore.