I don't think you would notice the difference in rolling resistance when pulling the trailer. There certainly are different opinions on tires (and wheels, and everything else) as the post above shows. For touring purposes I like wide tires. The wider tires let yu run a little less pressure, softening the ride, they protect the tire from pinch flats, and the rim from damage from potholes and whatever other road hazards you may encounter. The thing to remember when touring is that you seldom know everything that you will encounter-will there be miles of construction, or bridge expansion joints or transistions that hammer the bike when you hit them at speed, or a lot of dirt/sand/whatever on the road surface.
I use panniers on my bike, so the bike itself carries more weight, but I run 700x37's. Are they bigger than needed? Maybe, but I'd rather that than find out I was riding on less tire than I needed as it can be a long way between shops with real touring tires available.