I have floated many a time in my solo canoe, that is, a canoe designed for solo use with the seat in the middle. I have done many multi day river trips. Canoeing and camping go together and some of the best campsites are only available from a canoe. Many river campsites are not listed on any maps they are just there.
The design of a true solo canoe has it narrower in the middle so that the paddler can more easily reach the water. They come in various lengths including 17 feet long, just as long as a tandem canoe. A two person canoe is called a tandem.
With a tandem canoe, the commonest solution is to sit in the bow seat facing toward the stern, backwards. This put you closer to the middle of the canoe than sitting in the stern. This can be a problem if you have those molded seats. Since a canoe is symmetrical it can be paddled equally well in either direction.
The middle of a tandem canoe has a cross brace called the yoke. The yoke would prevent you from sitting or paddling from the middle unless it is removed in which case you can kneel and paddle or improvise a seat. Most yokes but not all are removable, you lose a bit of strength with the yoke removed but this is no problem unless you have rapids.
There are a number of seats out there that fit in the middle but Spring Creek Outfitters makes the best, see link. This company manufactures this canoeing item as well as many others. They also are a extremely good source for used canoes and offer a selection of items exclusively designed for fishing from a canoe. They are canoe outfitters, which is unique, so give them a look. They will let you make winter payments on the used or new canoe of your choice!
http://store.springcreek.com/Seats/Seats/Spring-Creek-s-Drop-In-Seat-With-clamps-p1577.html So...that's what you do if yu want to use your existing canoe. If you like to canoe a lot then you can consider a solo canoe. It's not so easy to find a used solo canoe but of course there are many choices for new ones. Minnesota is the canoeing capital of the world and If you come to MN in the autumn you will have your choice of used canoes maybe even a few solos. All boats, canoes included, are for sale in the fall