As the data is in two tables, it is impossible to compare that data without some kind of Link.
Personally, I would create a table called Days (if you are tracking single days) or Weeks etc., and then link from the Day to table A (relevant records), and also to table B.
Now your new table is pulling a rollup Sum(values) of the Estimate and the Actuals, you can probably fill in the rest (new column, calculate difference, plot as chart…)