Aluminum can be tough, but its cold, loud, and heavy. They are my least favorite. Poly isn't light but generally speaking, its near indestructible. Its good choice for a rough duty canoe. Fiberglass is difficult to pin down. The usual low cost, low quality chopper glass canoes are crap. They are slow, weak and heavy. A good laid glass canoe (visible cloth glass) can be a pleasure.
Wide does NOT mean stable. There are two kinds of stability in a canoe. Initial stability is how the canoe seems to feel with regards to tippiness at first. Secondary stability is how teh canoe responds to a lean as the canoe begins to lean farther and farther over. Many wide, flatter bottomed canoes SEEM to be stable. This is not necessary a good thing. Many of them have good initial stability (they seem stable) but very low secondary stability. In other words, and plain english, they seems stable as you lean them and do not feel particularly tippy, but once you get to e certain point they simply let go an roll over in a hurry. They give you a false sense of security that ends up rolling you over.
Many hinger grade canoes have somewhat low initial stability, and seem tippy. However, the farther over the go, the more secondary stability they have. They get BETTER as they go over. These do not seem so secure, so tehy encourage you to keep movement to a minimum, but when you make a mistake they don't roll you.
I would NOT personnally go for a 14 foot canoe. Especially if it wide it will paddle like a barge. Dad, two kids, and camp gear mean teh canoe will be overloaded, and it will be a beast to paddle. Look for a decent 16+ foot poly boat, of modest width. It'll take a good load but paddle somewhat easier.