Aluminum canoes are comparatively inexpensive and light and will last a long time, even if left out in the sun and weather. They are generally narrow in the stems and have keels, so they will track fairly well, and are flat-bottomed, so they have good initial stability. This makes them good for standing, poling, fishing, negotiating very small, mostly flatwater streams with deadfalls, getting in and out, etc. They make an good flatwater rental boats. However they are too heavy, slow, and noisy for most experienced paddlers to choose to use on flatwater.
They were used a good deal after World War II till the late 1970’s for whitewater, since they were tougher than glass and wood/canvass. However, even when outfitted with an unobtrusive shoe keel, their keels limit their maneuverability. The shape limitations of the material on the design of their ends and sides cause them to ship too much water. And they are noisy and tend to stick to and consequently broach against rocks they hit. They will dent and tear but can be banged back to the approximate shape and repaired fairly easily. These whitewater limitations are less important if their paddlers are very competent and confine their use to moderate class III or less.
I still have my 15-foot Sears aluminum canoe I bought in 1973, and it has been paddled several times each year since then. It has run Chattooga III and Chattooga IV many times. For some years it has lived chained to trees near the water. Perhaps my great-grandchildren will someday paddle it.
Aluminum canoes for whitewater were rendered obsolete by Uniroyal’s ABS in 1968. The first ABS boat was almost 16 feet, molded by Uniroyal and sold by many canoe companies under names such as the Blue Hole OCA, Mad River Endural, and Perception Nantahala and Chattooga. It is currently only made by Buffalo Canoes of Jasper, Arkansas and may be you best option. See: http://www.buffalocanoes.com/16_foot.htm
Mine has the standard aluminum thwarts and gunwales but the optional wooden bench bow/solo seat, which I strongly recommend instead of the standard black molded plastic one. My canoe weighs 65 pounds. It is a very comfortable and versatile boat, and I use it a lot for tandem and class I-III whitewater and poling. If you keep the hull flat, it’s quite maneuverable. If you lean one its side when paddling solo, it tracks fairly well and glides easily and at a fair speed.
Replacing a Discovery 169 with an Aluminum canoe is a reasonable option. Polyethylene weighs a ton and warps badly. The Discovery paddles pretty well straight ahead but becomes a chore when a lot of maneuvering is needed or if you have to carry it.