Hi Aminul,
Not sure if I understood your question correctly, are you trying to make more than one switch as root for different vlans in the network or do you want to see if you can load balance vlans on the trunk between the switches ?
In general STP (vlan) load-balancing is done when you have two seperate links trunking between switches, by default spanning-tree would block one of the ports. In order to effectively utilise the bandwidth between two switches load-balancing of VLANS is done so that few vlan can go over one link and few on the other .
Another way of utilizing the full bandwidth is by configuring etherchannel. So since you have already configured etherchannel between the switch the load-balancing is done based on the algorithm configured on the switch. you can use "show etherchannel load-balance" command to check the load-balancing algorithm on the switch.
If you are trying to make more than one switch as root in the network it all depends what you are doing on the core and distribution.
Since you have two distribution switches you can make one switch root for even vlans and one switch for odd vlans.
Hope this helps.
JayaKrishna
