I have trolled three lines out of one canoe before.  It can be done.  The "sweep" rods on either side are the bow and duffer and should be the longest rods you can get without being "noodles" that bend way back on a troll.  They should also be as near horizontal as possible.  The stern man holds his pole straight up by cocking the butt of the rod behind a foot or ankle and the rod rests against his shoulder.  The side rods run somewhat shorter lines and the rear rod runs furthest back.  Try to avoid sharp turns.

When you get a fish, try to reel in as little as possible while still retaining a tight line to the fish until the other two lures are mostly reeled in.