Budget Variance Report

I need to create a new report for Budget and Actual expenses by month and year. Business has provided the budget for the entire year divided into 12 months as an excel file. I get the actual expenses from APGL report. Now, need to create a DataSource & DSO for the budget file and combine that with the actuals to generate the variance report. Please help me with the design of the datasource and dso, with details of what fields to create in DS and DSO. Here is the output requirement.

Report Output

Here is the flat file fields of budget