Can Holley or MS3Pro do throttle by wire on the Buick engine ?

The answer is yes.

But the question is, "Why?"

Throttle by wire requires testing. Immense amounts of dyno testing. For throttle by wire to be better than a cable throttle, it has to be mapped to where throttle input corresponds to whatever combination of timing, throttle blade position, and fuel results in the desired torque output.

This is next level shit. And you're not going to be able to implement it without next level facilities and testing.