[VanVeen]

Bet the flop unless your opponent is only calling reraises with a relatively narrow range of hands. Most players call thin enough 3 handed in an aggressive game that this should be an autobet, especially if you don't plan on checking real hands with any frequency (generally a good plan in reraised pots). Given how you played it, there are relatively few hands in your likely range that have improved on the river. If you're perceived as at all aggressive and he has a tendency to call loose, this is a hopeless bluff.

If I bet I bet the pot, but bet sizes in these spots should 'work' within your overall gameplan. Don't leak information to good players. If a disporporiate % of your bets in this spot are bluffs because your opponents have a tendency to fold too often, I like smaller bets (60% of pot). The value you sacrifice when you're value betting is more than compensated for by the pots you 'cheaply' steal.