This is made somewhat tricky by the fact that opponent is in the big blind, meaning of course his hand range preflop is 100%.

I would want to call this if I could put him on a five. If the flop was 7s2s5x I would probably call this; however I do not see him leading into this field with just middle pair.

Why did he check the turn? This is (in my opinion) central to the river action (which is fold or call in my opinion). If he checked the turn cause he picked up open-ended to go with his pair and didn't want to be raised off it then this is a call.

It is tough to see a set or two pair checking the turn given the nature of the board. I think that (and the hidden nature of your hand) pushes this to a call.

Regardless, I think the key to analyzing this hand is "why did he check the turn?".