To take the guesswork out of it I just weighed everything and checked my cog and chainring.

I'm currently running a 44t with a 20t cog with the nexus 3-Speed.
I'm guessing the cranks are 172.5-175mm.
My bike weighs 55 pounds as pictured (no dogs) and has 20" wheels.
The diameter of the fat tires is nearly 26" (25 3/4").
The trailer + empty cooler weight is 33 1/2 pounds.

One big problem is I just measured the rear dropouts, they are only 120mm. I thought they were 135mm with spacers but they are not. So I am limited to the 3-speed hub AFAIK. So now the only option is to change the front ring or the rear cog. I can only gain up to a 23t in the back, so swapping out the front ring is probably the best choice. Probably don't need to drop down to a 32t though, maybe more like a 36t.