There are 2 'rims' that you visit. I think in March the 'north rim' will still be closed, but you should be able to visit the other 'rim'. I have never been to the north rim (it is the north side of the canyon). But be prepared for cold! It is beautiful up there. Here is a link for you to look at. This is quite an idea, but there is no way that I could walk on it. They would have to get the maintenance crew out there just to clean up after me :)!
http://www.grandcanyonskywalk.com/index.html