Hello cowii,
That's a very sick spot actually. Even if we at the best are against some pair+FD type of hand we wont get a good equity. And against even stronger hands we of course are far behind.
So basically if you even want to continue here then we likely have to ship it right here. But the question is do we really want that? Unless he really has some bluff-type of hands in his donking range then it will be pretty hard to get great equity against his donking range. And therefore I might even prefer at some spots folding. But now again while it's a 3bet pot and he seems to have some kind of higher AF then shouldn't be that wrong to get it in either here. He ain't even fully stacked.
Just to give a small overview how we doing against some range:
Board: 6♥7♥8♥
Equity Win Tie
UTG 71.12% 67.77% 3.35% { 66+, T9s, 87s, 76s, Ac8c, Ac7c, T9o, 87o, 76o, Ah8c, Ah7c, Ah6c, KhQc, Kh8c }
UTG+1 28.88% 25.52% 3.35% { QdQs }
So here you see we ain't really that much ahead and that's why I might even at spots prefer folding here to be better.
His line doesn't seem to be that weak either with his pot size donk.
Best regards.