This is my corrected post. I am not sure why I can not edit my post above.
Whenever I look to understand an optimization and how the numbers pull, I run a scenario analysis by varying the parameters on separate tax returns, then comparing the tax and benefit effect of each scenario.
First I run these comparatives in a single tax year on a base case.
Then a vary a few additional factors in a single year such a single, married, retired, eligible dependent, income split, pension split, etc.
Then I run these scenarios over time which helps me to understand the tax changes year over year such as the major changes to dividend types and dividend tax credit.
I run these as John and Jane Doe - T4 only.
I run these as John and Jane Doe - T5 only.
I run these as John and Jane Doe - T4 + T5 split.
I vary the T5 amount to understand at which income level T5 income becomes taxable. This varied substantially over the past 10 years.
For a really full picture I add up all the taxes payable for the base scenario including payroll, corporate, and personal. Then I show the variances.
I also add up the cash flow variances from the base scenario.
After that I take into account how client specific income slips affect the taxes due when the same T4 and/or T4 corporate slip is added.
Only then, can a specific client situation be assessed from based on a taxes due criteria only.
In other cases a base level of T4 income may be required for personal loan, personal mortgage, and credit scoring reasons. In this case the a fuller financial picture is required.
At this point I do not see how this can be automated. Rather I see how valuable it is to run the scenarios well before tax season starts in order to understand the variables and the financial model that is in play.