Can a co-author prevent me from submitting our joint paper to any journal except the one he prefers?
Jointly authored papers require permission from all authors. If he is a co-author and you can't convince him, then you are pretty much stuck. Editors will expect it.
And fighting with your PI is probably not the wisest career move.
It is a different story if the PI isn't one of the authors, but that only applies to the first point above, not the second. The &quot;we&quot; in your question wasn't completely clear about who is included.
It may not be too strong to say that a good letter of recommendation from your PI is one of the most valuable things you get out of a post doc. It lets you move on and get away from improper behavior. Winning a battle, but losing a war is sub-optimal.