Yes, getting there would be a much bigger hurdle, with the one exception of the much higher gravity. Be damned hard for us to build a colony in super high gravity, esp if we had no artificial gravity on the space ship for the journey.
Well we know that a fetus cant form properly in zero-g so we would have to have some sort of simulated gravity for any multi generational space travel. And once you have that, having it increase over the course if the century long journey would prepare the colonists for their new planet.
That also presumes that HD40307-G has a very similar structure as Earth. If its mantle or crust is less dense than earths or its core is smaller then its mass could vary significantly. Without knowing its actual (or rough) mass its difficult to predict its gravity. We can attempt to measure its impact on the other celestial bodies in its system but for all we know it could have a vast complex of voids beneath the surface that reduce its overall mass to one roughly equivalent to that of Earth and leaving it with a vary suitable environment for humans and earth plants.