My all my routers are Cisco Catalyst 3750 (in my testing environment). However in our live Backbone network we use Cisco Catalyst 7609.
So all are Cisco 3750 presently & i have set their priority as lowest (4096) compared to Mikrotik-CRS (8000hex = 32768) so that the core router becomes the root bridge.
But my core router is the root bridge & also the Mikrotik shows as root, leading to all ports to in DESIGNATED FORWARDING state. (not a loop free topology).
Note: All are connected by fiber patch-cords.
However in your case, CCR is good for routing purposes, rather then CRS...which is good for switching. Being which i'm still stuck here on STP !!!!!
Provide me a solution if you have