Hi Greg,
Seats come either with or without corner holes. On ones with corner holes, just run binder cane from corner to corner, forming a rectangle. Most often on seats without corner holes the cane simply makes a circuit all the way around, leaving rounded corners.
As for the flip, no worries. Most important is to get your canoe back to a place where you can enjoy it. Past repairs to seats are common and they often leave the seat frames with unpleasant fasteners, holes, and iron stains. Solutions besides flipping the frame include making new seat frames and spending lots of time on repairs. Old fasteners can be dug out, iron stains can be corrected (or at least attempted) using oxalic acid, and holes can be filled with epoxy and sanding dust. Just some food for thought but if you want to go canoeing, just do what makes you happy.
Michael