This is tough because I have no idea how Pro1 plays (apart from v well!!) and how pro1 perceives Pro2. I am struggling to put Pro1 on an accurate range given he called a big preflop raise OOP and is a good player. I feel inclined that he could be disguising a monster. How often has he 3 bet out of he blinds? How often has he called in the blinds? This lack of info and the betting (or lack of it - missed c bet on flop???) on the other streets is making my decision harder...
However....I"ll have a go...
In the past I"d probably have checked behind, but then again I do miss a lot of value on the river and as my new years resolution is to bet more on the river I"m going to look at betting here. The trouble is how much??
The trouble with betting here is that there doesn"t seem to be many hands you beat that would call a river bet. In addition your hand is struggling against the check raise on the river. However you are now beating most pocket pairs that haven"t made trips and his betting pattern does not neccessarily mean a flush.
In addition a 2/3 to 3/4 pot bet commits most of your stack while a thin 1/4 to 1/3 pot bet could be seen as weak and may get reraised for the hell of it. having said that the thin value bet may get called by a worse hand and if it is raised you can get out of there relatively cheap.
So, I"ll go for bet 1.5 million.....