I really hesitate to rain on someone else's parade, but I don't like that cannon. There are many little details that don't look just right to me, but the photos you posted aren't really good enough for a detailed analysis using the remote-viewing-only method.
Note that comments I make here are based on my evaluation of whether the cannon actually dates from the date on it, 1644, or not. If I think it was cast in 1644, I will like it, if not, I won't like it. It might be a nice model made much later, but if so that should be reflected in the price.
My suggestion is take the tube out of the carriage and get detailed macro photos all over it. I don't like the "composite" looking cascabel, the "16___________44" which is much smaller than a date on such a cannon should be, the sharpness of detail (lacking), the foliage just behind the muzzle swell, etc. Need good photos of the dolphin and trunnion areas. Need photos of underside, etc. etc. Glad to help, I've seen more of these small cannons than I can count, and bought just a few. Why does the vent look like the material changes down inside of it? The trunnions look like they have rimbases, and no real bronze cannons or models of them (that I know of) of the "1644" era had rimbases. If the whole thing, dolphins and trunnions and cascabel, wasn't cast as one single casting, it is almost certainly a recent item intended as a decoration only. The carriage shows few if any signs of age.