it's really not going to matter either way. whatever you are most confortable with. if he decides to come up with you and the kids, then it's important to make sure you all use the right langauge at the border. he is only visiting until approved as pr. CBSA will not have a problem letting him in as long as he understands this fact. bringing a copy of the pr application, receipts for fees paid, copies of correspondence from CIC (sponsor approval letter), and proof of ties to the US will also help.
More than likely, based on what current US applicants are facing, there is a good chance he'll be approved by august and he'll be able to land when you go up.