Here is a common design that works. If you don't like this design, get creative!
Use two 2x3's 92" long. Duck tape to canoe braces while ensuring canoes are parallel. At Front or Rear brace, 92" struts should extend to edge of canoe.
3/4" plywood platform: small: 32"x45" or large: 32"x72"
Screw plywood platform to the 2x3's.
Mid-struts: A long platform needs 2 or 3 mid-struts for support. Made from 2x3's and 34" long, they are screwed to the platform. The strut ends just rest on the canoe edge. For a level platform, pad the 1.5" mid-struts out to 1.7" or 1.8" thick where they rest on canoe edge.
If you make a small platform from 3/4" plywood, 1 mid-strut is enough, or no mid-strut if you're feeling lucky.
Handle cut-outs are nice. Sand the wood to prevent splinters. Polyurethane makes it last. Staple or glue outdoor carpeting.
Do your bottom a 15 hour favor. Bungee comfortable patio chairs into the canoe. Folding sling chairs or white resin chairs.
Front chair can straddle the 10" high bench if its legs are long enough (saves space). Face it backwards if the seat is at least 15" high.
Rear chair can go just behind rear brace if the front edge of seat is 15" or higher. Best if rear legs are no wider than appx. 21".
Low chairs don't work well. Canoe braces interfere.
Don't forget the drink holders.