My experience with Minwax Wood Hardener was as I was trying to find a way to make wooden baits more waterproof, not for strengthening, but here's what I learned.
The wood hardener penetrates deeply into the wood, reinforcing the cell walls, because it was designed to help make rotten wood strong enough to paint again. I found that when I soaked a wooden bait in the hardener for an hour, it would penetrate so deeply that it took a week for it to stop giving off solvent fumes. This made it a big delay in the painting process.
If I were making a big balsa bait, I would worry that a penetrating sealer would take away the biggest plus from using balsa, it's buoyancy. The more sealer that's absorbed, the heavier the bait will become.
If you're looking to strengthen the balsa enough to make a 10" musky bait, I worry that you will have to do so much strengthening that you'll lose the buoyancy and lively action that is balsa's distinguishing feature.
I would suggest that you explore other woods, like poplar, or even go to a PVC decking material, which is buoyant, but still strong.
I stopped building lures from wood, and switched exclusively to PVC, except for small balsa cranks which I harden with super glue on it's surface.