Acrylic gel medium seems to be recommended a lot. It's what I'm using now after trying a lot of other things. I adhere the paper to gatorboard then treat with wax or acrylic spray varnish so no glass is needed.
I suspect that wall paper paste would work just as well, wouldn't yellow and would be easier for conservation purposes. Could be steamed off. And would be cheaper. And even if it yellows it might not show.
For collage purposes the acrylic gel is probably the way to go.