I've never been a fan of Mantua kits, but this one does look reasonable. The shape of the gun muzzle looks a little odd, and the turned details on the barrel probably are simplified compared to any real gun of the period. But the proportions look about right, and the price is reasonable.
Several other companies make naval guns, some of them in diorama-like settings that can be a lot of fun. Here are a couple that might be of interest. Smaller scale, and cast resin rather than metal, but the prices are right - and everything from Verlinden that I've ever seen has been a first-class product.
http://www.squadron.com/ItemDetails.asp?item=VE1898
http://www.squadron.com/ItemDetails.asp?item=VE1904
Here's a page from the site of the Saratoga Soldier Shop, distributor for the fine, long-established American military miniature firm of Imrie-Risley. These are white metal kits, which need to be assembled and painted.
http://www.saratogasoldier.com/irkits_seamenbritish.html
Unfortunately there don't seem to be any photos of the naval guns on the site, but if you navigate from that page to the home page there's a link to order the company's printed catalog - which does have pictures. I/R has been in business for a long time (close to fifty years), and its products do vary in quality, but my recollection of the naval gun series is that they're quite good. I built the carronade quite a few years ago; it was a fine, well-detailed, accurate kit.
It's a shame that no plastic kit company has seen the potential for historical cannon kits. The only ones I can think of are the Napoleonic guns from the French manufacturer Historex - beautiful kits, but decidedly non-naval.
Many, many years ago a now defunct American company called Palmer Plastics did a small range of guns, including a Civil War field piece, one from the American Revolution, a French 75 from World War I, and a generic naval gun from the sailing ship period. My recollection is that it was pretty crude and of highly questionable accuracy. (I do remember the "brass plated" barrel, which came in hollow halves - and presented an insoluble joint-filling problem.)
For a while those kits were available as mail-order premiums - price: 50 cents, plus a coupon from the back of a Quaker Oats cereal box. (Remember: "Nutrition, flavor, and lots of fun/from these weight-watcher cereals shot from guns [BOOM!]"?) I think they may have turned up in Life-Like boxes later; I seem to recall selling a few of them when I was working in a hobby shop in the late seventies. But those kits are a part of hobby history that's better buried and forgotten.