I have two methods of anchoring the posts to the pier that might work. 1: stick a piece of rebar in the concrete before it sets up, leaving a few inches sticking out and drill a hole in the bottom of the post that will slip over the rebar. 2: They make an bracket (designed for 4x4 or 6x6) that has a rod in the bottom and a C shaped bracket with a hole, that recieves the post.
A BETTER WOOD POST-rather than use treated a 4x4, 6x6 etc. I believe it it better to laminate several 2x boards together by screwing in combination with waterproof construction adhesive. The finished product has treatment all the way through, resists splitting, warping, and starts out straighter.
