I’m lucky enough to have a professional furniture stripper within a few hours of me. I take 4-5 canoes at a time. I take out the seats and long decks if they are there. It helps the stripper do a better job.
There was a time that I did strip my own. It is time consuming, tedious, and the result was not near as good as the professional. It costs about $20/ft these days. To me it is worth it in the time savings, quality of the end result, and cost of gallon cans of chemical.
Check the commercial stripper in your area... it may pay off.
If that’s not feasible, I recommend getting the most expensive, harshest stripper to remove the old varnish.
I’ve tried to do it on the cheap and environmentally safe, but the results were not good.
I always say with strippers, varnish, and marine paints....you get what you pay for.