Resistance is resistance, friction is friction, whether it's from added weight, extra wheels, wind, gradient, whatever. You have to push those pedals around one way or the other. More resistance?, you either slow down or you get a stonger motor.

Personally, I tow a trailer because I despise how a loaded bicycle handles. So I tow a two-wheeled trailer and probably wouldn't even tour if I had to go back to panniers. I'd rather ride a bicycle than feel like I'm driving a truck.