Party spokesperson: The opposition party’s proposal to stimulate economic activity in the province by refunding $600 million in provincial taxes to taxpayers, who could be expected to spend the money, envisions an illusory benefit.
Conclusion (So)
There can be no resulting net increase in spending to stimulate the province's economy.
Intermediate Conclusion
Let's say we refund $600 million in taxes to taxpayers --
We would then have to either 1. raise new taxes (defeating the purpose of the refund) or 2. government workers would have to be fired
You're either putting $600 million in the hands of taxpayers or keeping $600 million in the pockets of government workers who would otherwise need to be fired.
Evidence (since)
The province's budget must be balanced.
Evaluate
Given that .. it's $600 million, either in the hands of refunded taxpayers or not-fired government workers.
How could we say that .. there could be a net increase in spending to stimulate the economy?
This is a question where outside knowledge can help. When politicians debate whether to give tax breaks to wealthy people/corporations vs. give money back to lower-earning taxpayers, it's often remarked that the wealthy companies and people are more likely to save that money, whereas the less wealthy people need the money for so many things that they're more likely to spend any refund money they receive.
Goal
Hard to predict where this is going, so we would just think, we need an answer that plays along with the constraints the author's premises laid out, but gives us a way to say that there could be a net increase in spending / stimulating.