I've been a canoeist for about 40 years now I have come to a few conclusions.
I've had fiberglass, almuminim, Royalex, and now kevlar. I started out with a fiberglass Mowhawk, went to a Grumman aluminum, then two Old Towns in their ABS layup, now a Wenonah Kingfisher 16 in lightweight kevlar at 38 pounds.
The Wenonah is the most money I've ever dropped pin a canoe. But it makes me regret the money and time I wasted on the Old Town's and other canoes. The on water performance, the very lightweight easy handling inland, and the hull design is very worth it. It really is true that you get what you pay for. My Old Town Camper was a good boat, but it does not hold a candle to the Wenonah Kingfisher. For a fishing and all around recreation boat, you do not want to go too short. 15 to 16 feet is a good sue boat. The longer hull will give you easier paddling, more speed per paddle stoke, and more stability. A 16 foot canoe will be very noticeably more stable than a 12 foot canoe. At 12 feet, a canoe is way to small for just about anything except for a kid playing around on a small pond. IN fact, old Town makes a canoe called the solo at 12 feet, and it's rated very low for carrying capacity.
If I've learned one thing from a life of canoeing, it's don't try to save money on a boat. Buy the best right off, so you don't have to suffer with a pig on the water. Royalex, or what they call the ABS laminate is heavy, and makes a blunt hull design. Aluminum is very noisy, and is called boomers because of the noise they make when a paddle hits the side, or you move around in then, or anything.
I regret the other canoes I had, and if I were doing it all over again, I'd go with the Wenonah and save myself the time and money wasted on the 'other' mediocre boats that spend a lot of money on advertising.
I have seen old town canoes made with Royalex survive situations that would have destroyed canoes made with other materials. Kevlar was just hitting the market on very high end canoes when I was spending time on the water so I don't have much experience with that stuff.
Everything so far has been excellent advice.
Let me add:
Make sure you buy a canoe with as much freeboard (side height) as you can afford. Makes the canoe more forgiving.
I miss my canoe but kept the custom made Ash Paddle!
I've had 2. The first was a fiberglass one. Very light. Easy for 2 to handle. My most recent was a plastic one from Dick's. 14' 3 person. I did find that exposure to the sun can cause the bottom to warp. It hasn't effected its float-ability though.
I agree with one of the previous posters on the Kayak, but I would recommend a single for each person unless you're taking a kid that is a bit young. kayaks refer to Tandem kayaks as "divorce boats". I started in Canoes since I was 8 and had them up to several years ago and I switched to kayaks and would never go back.
Canoes excel at hauling thing as they have displacement hulls. I used to have a Old Town Discovery 169 with the Royalex hull and it was flat out tough as nails. It was heavy too and you can't handle that large hull alone under paddle. But I had 4 150 pound people, 2 coolers (one food and 1 beer) and camping gear on the Potomac before. Like I said they excel as hauling things.
Kayaks are better for fishing. They are faster, lighter many times, have better seats. The new ones are 10 times more stable than a canoe. Rookies can stand in some of the new kayaks. I have a Wilderness Commander 120 and Ride 135 and use them for hunting and fishing on the river and the bay.