This is a common problem with adopted babies, most of whom have had
bottles and pacifiers before adoptive placement.  My last two children
would root, but my daughter would only open a tiny bit and my son would
pucker his lips as though he was waiting for someone to push a little
pointy nipple into it.

I tried all kinds of things to get them to open up, all to no avail.
The best thing I was able to come up with was to line up their upper
lips with my areola, "flip" the breast into their mouths as far as I
could get it, and then immediately pull out the lower lip and push down
on the lower jaw, to get them to suck in more of the breast.  Neither
child ever really opened up very well, but it did become easier to latch
them on as they grew.  It would have been easier if they had opened
their mouths, but we did pretty well with this method.

Aloha,
Darillyn