Is it possible to setup and wireless bridge with a RB2011UiAS-2HnD and a non-Mikrotik AP? I have an Asus TM-AC1900 and would like to be able to roam between these two APs seamlessly. I don't have Ethernet I can connect them with so I need to bridge them wirelessly. Can anyone point me to a guide or documentation that might help get me started?

No seamless roaming is possible. If your Asus supports wds bridging and virtual Ap or some "repeater" mode, it is possible to use it as extending Ap. Always use wires instead radio waves. Consult your user manual for Asus device capabilities.