CJ should be on an unguaranteed contract for the Blazers next season, if reports are correct.
The Celtics should seek someone like him though. They could use an athletic shotblocker off the bench, but need one who is a better rebounder. They're not going to find that among established free agents, so they're best chance is to find one with a raw offensive game toiling in the D-League or as an undrafted free agent.