Hi,
Winslow goes up and down stairs all the time, yes, you have to be careful while Training a newf on steps, but you really should get them some experience with steps. You will encounter steps in numerous locations while with your pet and trying to get a 100+ pound stone to do something it doesn't know how to or want to do will be a problem.
Going to the vet, or a groomer, or into a home, or out to the yard. A few steps are always presents somewhere. If you train your Newf they are fine on steps you just need to be sure there is some good traction on the stairs so they can't slip.
Rich
PS you can't force them just praise and encourage them to get up and down on their own. Winslow took a few months and some peer pressure from another dog before he made the first climb.