The best way to do this would probably be to use either a parameter--although this option only allows the user to make one selection at a time. The parameter would contain all values of the Campaign field. Then, two calculated fields--one for each source--would need to be created for the parameter to work in each view. Each calculation would look similar to the following:
Then, place this on the filter shelf and select True.
The other option would be to use actions--create something similar to a table of contents:
For this, you would need to inform the uses to hold the Ctrl button and click to make multiple selections.
Hope this helps!
if you need multi-select filtering you can use another worksheet on the dashboard to act as a filter by using Actions. You will have to setup the selected fields option to filter across data sources. post an example packaged workbook it you would like to see an example made for you.