Consider making a shoe for the bottom of your mast from 2 piece of 2x6 or 2x8 about 9 inches to a foot long. You really just need something to spread the weight and pressure over a reasonably large area of the hull to avoid puncturing it.

Stack the two pieces and secure them with nails or screws. Drill a hole in the top piece to hold the bottom of your mast. Shape the bottom edge of the bottom piece so it conforms to the curves of your hull. When the mast is set in place the shoe may slide a bit, but the fixed rigging on your mast should limit that movement.

Use a 2x6 or 2x8 board like a thwart, but clamp or screw it to the gunwales, and drill a hole in it for the mast. Slip the bottom of the mast through this hole, and engage the "shoe". You can attach wires to the left and right sides of this board for fixed rigging (stays) to support your mast, or you can tie this rigging to some other place on your gunwales. Connect a forestay to the bow of the boat. Tighten things down and it should be pretty stable.

To shape the shoe to the inside curve of your hull. Start by scribing the hull shape on the wood. Remove as much as you can with a hand plane. Final fitting is done by sanding. Use rubber cement to hold a full sheet of 80 grit sandpaper (grit side up) to the bottom of your canoe, and slid ethe "shoe" along this area, putting pressure on it, until the excess parts of the wood are abraded away and you get a good match. It may be boring work, but it is not too difficult or too time consuming. If you use cedar or some other soft wood the sandpaper will do the job quickly.

Peel off the sandpaper and rub off the dried rubber cement.

A layer of some compressible, non-slippery material sandwiched between the shoe and the hull might improve things. A sheet of 1/8th inch cork, or maybe 1/8 to 1/4 inch neoprene fabric (like on a wet suit) might reduce sliding of the shoe, but leave no adhesive residue behind.

hope this helps.

PGJ