When paddling stability primarily comes from the shape of the boat, body position in the boat (e.g J leans), low centre of gravity, and keeping the boat in motion (just paddling). There are times when you may want to provide a bit of extra support - when people are getting in/out, launching, rescues, moving around the boat. There are two methods that I use to provide just a bit of extra stability - Sculling Brace, and a Dropped Skeg.
This brace is done by sweeping the paddle across the surface of the water, with a slight upward pitch on the blade. This motion provides an extended outrigger for supporting the canoe through the body and preventing the canoe from rolling or tipping to the paddling side. Choking up on the paddle allows more extension and better support. The paddle is extended over the water with the grip hand fingers under the grip, and the shaft hand on top. Although the strongest brace is when the paddle is almost parallel to the water surface, this is not usually necessary until more support is required.
The support is on the paddling side so in a tandem boat you may want to augment this brace with a dropped skeg or low brace on the other side.
If the canoe is in motion the 'sweeping' motion can be replaced with a static stroke beside the paddling station, or a little back, with the blade skimming the surface.
This stroke is used to stabilize the canoe countering roll and side drift. It is initiated similarly to a righting pry, but held in place next to the canoe instead of completing the pry. When held in place the blade should be in line with the length of the canoe - very much like a keel on a sailboat or skeg on a kayak. I usually slice (drop) the paddle in from the back but there is no reason that it can't be sliced in from the side and rotated when it meets the hull.
The blade provides resistance to motion, preventing roll or sideways movement. The blade must be fully submerged and held in place, with the grip hand at chest or armpit height. The recommendation I have been given is to hook the shaft hand thumb over the gunwale (locking the shaft in place). The shaft can be pressed against the hull by pushing the grip hand out (slightly) for more support. To be honest I have some concerns about using the thumb hook as I think it can put a lot of force on the shaft hand thumb, with potential for a dislocation.
The Dropped Skeg is extremely effective in limiting the amount of roll experienced by the canoe and can be used when the canoe is stationary or in motion. This is not a bracing stroke so it will not be useful if the canoe is tipping - although transitioning to a righting pry (if tipping to the off side) is easily accomplished. Deep water is required, I have had a couple of tippy feeling moments when the blade hit the bottom or an underwater obstruction (rock).