Sure it'll cover it fine, you'll possibly need 4. 2 at the house pointed at each structure and one at each structure. The signal pattern on the engenius ens200 probably isn't wide enough for a single one to sit pointed between the two structures and get resonable signal gain from them.
For the expense though, so long you don't mind a small amount of work, why not just trench and do some direct bury ethernet cable? Cat5e direct bury is pretty cheap for those distances and its probably only a weekend of work to trench and bury 2ft deep for both structures. Or you could go even shallower if you aren't too concerned about it.
*EDIT* by some, how many are we talking? A tree or two? Or are we talking possibly a dense stand of trees blocking the signal path? If the later, it will probably still work over that short a distance, but it is going to cut the signal signficantly unless you can raise the antennas up above some of that.
One tree through the trunk is the equivelent of several interior walls in a house, especially a thick tree. Higher up through the canopy, in the winter time, it might only be the equivelent of a single wall, but leafed out it might be the equivelent of a couple of walls.
It just depends on how sparse or full the foliage and the canopy of the tree is. Pushing through several trees, fully leafed out can really kill a signal fast...though for only 45m, it would probably still work okay. Like a lot of things, you wouldn't know until you try.
I still recommend trenching and running cable, in part due to the relatively short distances involved. It looks like 500ft of cat5e direct burial cable is around $100. So all you'd need is the 500ft of direct bury cable and a pair of inexpensive ethernet switches to go in to those buildings instead of, probably, 4 APs at around $65 each (plus associated wiring for them and possibly a switch in each building as well).
Probably cheaper to direct bury, if you don't mind a weekend of work.
