Hi,
if possible, use a routed core and not a layer2 core. From a spanning tree perspective use multiple instance spanning tree, which gives great convergence time with minimal impact on your switches. Make sure SPT root and HSRP active router are on the same switch.
Other than that it depends on your exact traffic flow, what is possible and what not.
Load sharing is more tricky than most people expect. It can be adjusted f.e to do load sharing by src IP, dst IP, include layer4 information, based on MAC (src or dst) and so on. Depending on your network and resource distribution default settings might or might not work. We would need further information to give a more precise advise (admitting that I might cause more confusion than clarification in mentioning all the above).
In any case, never expect a perfect 50:50 load sharing. Some load can be distributed across one switch and some through the other.
Regards, Martin
