+xAs PLA is not great for releasing from, you may want to coat with epoxy resin, then sand smooth and polish to a gloss. You would then have a non-porous smooth surface ready to take any release agent. If casting the PU resin, then go with the CR1 for ease of use.
I actually printed all my tooling from PLA so far and never had any issues. I used a wax release agent. Never aimed for a very good finish tho so always had a heavy coating of wax on it.