You can check multyway here. It depends on the info you have on the villans. If they are both weak players, I'm going for a cbet, if they are both regs I'm checking because they should have strong ranges, when MP calls an UG open he should have a very strong range. As played I like your check ott and river we have to go for a value bet, he has worse spades that will check behind. If he goes for a bigger raise, I'm folding with no info. When he goes for a min raise, nothing you can do.

x/r river (as was in your title) would be leaving plenty of value on the table just as the other commented indicated, there are spades that would call behind. I expected the villain's range to be significantly stronger than he showed up with, especially considering he called a UTG open immediately to act after. With that, I expected to see pocket pairs or suited broadways - which easily could have a spade to call river.