I create my own topo/Google Earth composites using "Canvas", and would buy an iPad to use them in the field for archaeology if I knew I could get such an app.
No, I don’t know how to do that. Your point is interesting though, because I also take google satellite images along when I go, simply printed on card stock and laminated. The google images allow individual trees to be resolved along my path, but I don’t get elevation. Several miles of my trip fits onto one page, so between them, I’m set. But I’ve wished for an all-in-one solution, as google empties the photo cache when wifi service ceases. I’ll check again next year for upgrades to Topo that might allow that.