Easel G-Code will run on a Marlin MPCNC without modification. No editing is necessary. The G-Code output by Easel (free version) is extremely simple/basic. I authored about a dozen different cuts using various Easel features and shapes and found only five different g-codes used in the output files: G90, G20, G0, G1, and G4. So basically setting absolute coordinates, setting values to mm, linear moves, and a ‘dwell’ at the end probably to make sure the queue is clear before exiting.
The home position is fixed to the top of the stock in the lower left corner. There is no form of spindle control prompting, so the router must be turned on before the file is executed (or the file edited to add the control). Or if using Repetier-Host, I believe you could just create a custom printer with Start/End code for spindle prompting.