Unpaved trails tend to be slower on a trike than on a 2 wheeler as the 3 tracks tend to slow one down. Some of the trails either have only 1 narrow clear path or 2 clear paths (no grass or loose material) these really slow you down and take much more effort. I did the C&O several years ago on a trike and it had quite a lot of distance where there were 2 clear paths but the center was grassy and higher, I had to ride with either the rear wheel in the high center or both front wheels in the high center and the rear in one of the low tracks.
I have toured a lot on my Greenspeed GTE trike, (a very wide tadpole trike) the only issues I have had are
1. on a bridge where you needed to use the sidewalk, the sidewalk at the top of the bridge became too narrow for my trike to fit. (this was not on an ACA route). (South Grand Island bridge near Buffalo, NY)
2. Temporary bridge closure having a shuttle bus across a nearby bridge that didn't have pedestrian/bicycle capability, the shuttle bus could not accommodate the width of the trike, causing a 20+ mile detour, (I don't know if it was on a ACA route, Maine/NH border). I knew of the bridge closure and had planned for the possible need of the detour.
3. A ferry between Salem and Boston, trike was too wide for ramp and had to be lifted over the railings several times. (not on ACA route).
When I looked into the Ferry for Key West to Ft Meyers, I was told that my trike probably would be rejected as they didn't have space for a non folding trike. This was several years ago.
So with the possibility of the unpaved trails being more unfriendly for making good progress I would not consider most routes to be trike unfriendly unless they involve detours or restricted ferries.
