D., hey...take a deep breath. Yes, he's doing it out of anger. You're right. But he's just 3 years old. He's got a brand new sister. He's no longer the only child, the baby of the family. He's still trying to adjust to life as the firstborn, not the baby. Little sister gets to pee in her diaper, so why can't he get that kind of attention anymore that you lavish on her while you change her diaper?
Before you try any techniques to alter his potty behavior, try finding a way to give him more attention that is not potty-related or discipline-related in any way whatsoever. You can TELL him he is loved just as much as he was before baby sis came along, but he's not going to understand, accept or FEEL this until he gets something tangible out of it. Get him feeling more loved and adored again, then when he's calmed down, try to gently remind him that big boys (like Daddy) all use the potty and don't pee on themselves.
And hey -- if candy will get him peeing and pooping in the potty again, give it to him! Pick your battles. You can try working in a different kind of treat if you are afraid of the sugar. Does he like cheese doodles? Yogurt bites? Fruit? Little cheap party favor toys like plastic cars? These come in blister packs of 4 or 6. A couple of these cheapo toy packs will last a couple of days, and if you vary the kinds of rewards he might get -- surprise him, in other words -- he will seekt the reward more frequently just to see what he will get next.
Get some help with the laundry, etc. The kids themselves are way more important than anything else.
Remember the poem they used to give all new moms? It ends with the lines,
"...and children grow up, I've learned to my sorrow.
So quiet down cobwebs; dust, go to sleep!
I'm rocking my baby, and babies don't keep."
Your boy is crying out for attention, and that's not a bad thing. He's using the one thing that seems to be most important to you right now -- the potty -- because he can't tell you in words.
So go easy on yourself. Kids' maturity isn't a straight line. They progress forward, they regress backward. Then they go forward again. We adults have similar cycles. It's a human thing.
Peace & cyber hugs,
Syl