Displaying two different maps simultaneously is not possible. There is one map active for calculating the route (see red arrow) and you can have one overlay map active for planning the route (see blue arrow).
Menubalk met overlay.png
I suspect you mean whether it is possible to compare or view multiple routes on the map. The answer to that is yes! Below are various links to the relevant instructions:
Manual 'Compare Route Calculation' (Gold)
Manual 'Display and Merge Multiple Routes'
Manual 'Compare Tracklog with Route'