I can't really speak to proper etiquette or technique, but a basic leapfrog system seems to work for me going solo. It's just a series of small bites.

I usually double portage with a main pack and small daypack in addition to the canoe. On regular routes/portages, I take the canoe and daypack first, then return for the main pack (I tend to travel a bit heavy since I often bring extra photo gear).

When bushwhacking I reverse the order and take a pack first so I can scout out a path. If the going gets extra tough, I'll just take the daypack. In any case, I just go far enough to keep my bearings before returning for the canoe and the rest of the gear. I can usually leapfrog segments in two trips, but some of the thicker stuff requires three (like when crawling over nets of deadfall).

I personally don't leave markings, but then again I don't usually go too far between 'leapfrogs'. I do bring a GPS to record a track, and occasionally I will use it to keep my bearings. Generally speaking, though, the more difficult part for me seems to be about finding a way through some spots and less about knowing where I am. The GPS is a crutch that I try not to rely on, but I know it helps - probably more than I care to admit. I'd like to wean myself of it as I gain more bushwhacking experience.

To a limited extent I can see using an axe or saw to help get through some tough spots, and there's not much damage a solo bushwhacker can really do anyway that won't soon disappear, unless they're spending all their time hacking away at it. But to me, bushwhacking seems more efficient when you just squeeze yourself through and push on. I think of it more as a oneway trip - the quickest/most effortless way you get through to the next step the better. I'm not thinking about making a trail to return on. I imaging one could waste a lot of time and energy unnecessarily trailblazing.

For those traveling in groups, I imaging that it would be of great benefit to be able to crash through in a single trip. This obviously puts a heavy burden on the 'trailblazer' in front. I recall this is what Hexnymph's group does. I don't remember if they give the lead lighter gear to carry, but I think I recall them saying they at least rotate out the lead on a regular basis.

I'm far from an expert on the subject. Just my current thoughts from limited experience.