Hero actually raised to $225 total. MP1 went all-in for about $425 more. MP3 folded. Pot now about $1215 (including MP1's raise). Hero?

About my raise here on the flop...
I put MP1 on a pocket pair 22-TT, but most likely 77 or 88. I was worried about a set but I thought it more likely he just had an overpair or maybe the flush draw. If he put both MP3 and me on two overcards, his bet makes sense. My hand seemed well-disguised because of my just cold-calling pre-flop, so someone with 77-JJ was likely to play with me.

MP3 I put on JJ or A high flush draw, maybe AA or just AK.

My raise of $175 offers any potential callers almost 3-1 pot odds. Anyone with an A high flush draw has 14 outs (8 spades, 3 aces, 3 fives), about 2.25-1 odds. So maybe just calling and waiting for a safe turn card would have been better.