If you like XFCE and would like to continue using it, you could configure the tablet by using the xsetwacom command. You will need to have xf86-input-wacom and input-wacom packages installed (one or both might only be available from AUR).
This page should have workable solutions for your needs: https://askubuntu.com/questions/839161/limit-a-graphics-tablet-to-one-monitor.
I’m using a Wacom tablet myself on XFCE as a mouse replacement for my daily driver in a dual monitor setup. However I am using it in relative mode (acts as a mouse instead of being mapped to the monitors).