His plan was simply ludicrous.
He poisons Brock somehow with a plant that has similar effects as ricin. He then has the ricin cigarette lifted so Jesse thinks it was Walt so he would go and confront him.
He then hopes he can trick Jesse into believing Gus poisoned Brock to frame him. It's a crazy plan
His plan to kill Gus is equally as crazy. Hector has to hate Gus enough to agree to blowing himself up, tyrus has to be watching the dea building, Gus has to hate Hector enough to walk into a trap after showing almost supernatural levels of paranoia to avoid the car bomb.
Yet it all falls into place. Walt is a good judge of a person