my juicy 3 piston is seized,any good ideas on how to free it up?

remove the pads and hold the other one in with a flat blade and pump the lever sometimes frees things up.

Take the pads out. Hold back the 'free' piston with a flat screwdriver or metal tyre lever. Pump the lever. Should free it.

You canuse a drop of DOT 4 or 5.1 fluid to lube it or a silicone lube – like plumbers use on push fittings.

Just don't pop it all the way out – they don't travel far without coming all the way out of the caliper body.
2 1/2 pumps of the lever on mine from the piston being all the way in the caliper. 3 would pop them out for sure.
When you get it moving, wipe and then lube the exposed piston with some DOT4 and press it back in. repeat until both pistons move equally, this can take some patience !
I ring spanner works well as a lever to push the piston back without damaging the centre peg.