Auto labeling of variance between Stacked Column

Dear all,

My knowledge on Excel is still very basic so please bear with my ignorance.

Currently my job requires me to present a monthly sales report and requires me to present the sales level for 7 different products (Using Stacked Column) in 3 different years (So there will be 3 columns). Now my question is i have to show the % variance comparing between columns for all 7 different products and is there anyway to automate and display this variance data in the graph? Currently this process is done manually and takes up alot of my time. Attached is a sample of how it looks like as the end result

Please note that currently the graph is done on powerpoint but i can revert back to excel if there's a solution to my problem.

The solution i'm looking for is just a method to display variance (in %) between columns. It does not have to look similar to what is currently done. I am open to all forms of suggestion and possible solutions.

If such task can only be completed with an external add-on software, i will appreciate if you can also point me to the right direction.

Thank you all for your help.