It is being calculated on overall fossil fuel consumption which is easy enough to measure.
Not by each person. What if you don't drive? Why would you qualify for any rebate?
What if you drive a lot? Then the rebate should be higher?
The only way to make it revenue neutral would be to claim all the things you buy that are subject to this tax and get the rebate as a percentage of that. And if that would be the case. What would the point be? It's just an extra level of government.
Also, HST is collected on top of the Carbon tax. A tax on a tax. So it's pretty much a Tax Grab.