I would like to aggregate multiple WAN links. I have looked at mptcp but not sure if it supported on RouterOS. This is the scenerio. I have three DSL connections at 3mb each. I would like to create some type of VPN tunnel to my DC and have 9mb at the LAN side of the mikrotik and 9mb at my DC.

If you don't have control over both sides of the DSL connection (which you probably don't) you can't aggregate to have a total of 9mb. The best you can do is load balance, and PCC works as well as ECMP.