The maximum critical resistance is 7518 or 110% from gear, trait, and CP. This is not a hard cap; it is the maximum that can presently be stacked in the game.
The maximum critical damage modifier is 115%, like wise from gear, passives, and CP.
Therefore 100% mitigation of critical damage is presently not possible.
Stacking for maximum critical resistance isn't recommended since the gear and CP trade-offs are so great that such a build would be severely restricted in damage output and sustain. That's why many players are satisfied with 2k to 3k critical damage resistance.