My brother wants a truck bed extender to haul his 17 ft canoe. I don't know much about them but I was hoping you guys would and could help pick out a good one for him.

You might want to read this thread about using an extender to carry a canoe without putting it overhead: thread. Not sure if the person has tried it yet.

Also put extender into the forum search. Many of the threads are about overhead racks.

There are a number of those options on the market. With that said, I would try Springcreek first. Chuck is very helpful/knowledgeable and phenomenal customer service. I don't use a bed extender, but have purchased other products of theirs and have been extremely happy. I learned about them from this site. See attached link.

Mike

Spring creek dual purpose rack

Years ago I purchased a truck bed extender from Cabellas. Use it often. It works great for hauling our 17 foot canoes. It beats overhead for short hauls. Be sure to tie a flag to the back of the canoe to warn motorists that are behind you. It will only work well with one canoe. The canoe will be right side up so it will catch rain water. At our cabin in Canada, we use it to carry the canoe to other lakes. Today, I will use it to haul some longer lumber.

If he wants to do it on the cheap, then this and that will do it.
Using the cargo bed tie-outs on each side of the bed will keep the extender from free play/swinging from side to side at higher speeds of interstates. (Similar to 2nd pic shown of the Darby roof rack.)
Worked fine for me until I was able to purchase a pair of bolt-on racks for the truck bed.