You can make a menu screen, with easy/medium/hard button, on button clicked set variable:
Easy - Cards 6, Rows 2, Columns 3
Medium - Cards 12, Rows 3, Columns 4
How to set variable?
Add Action - System - Set Value - Than select your global variable, and type the value... :)
After set of all the card, row, cols, you can use the Action - System - Go To Layout to start the game.