100% Critical Chance

Should be possible... Leia, for instance, has a base chance of about 38%. With set bonuses she goes to 53%. If she has optimal primary and secondary stats, you can easily add another 42% to bring her to 95%. Then her leader ability would bring her over 100%.

I suspect it would be pretty difficult without a leader or unique ability. It seems the maximum secondary stat for crit chance is 5%, and I believe the crit chance triangle is 12%, meaning you can get a max of 57% from mods.