Yes. it's possible but it doesn't work right now with Mikrotik - I've tried to use versions from 2.8-2.9.40 as a load balancer - it worked but connection have been dropped until few minutes and doesn't balance traffic correctly. It's strange cause regular Linux with patches and all additional features balance traffic exacly in the right way (no drops, no hungs). I use NND Linux as load balancer (nnd.freesco.pl - it's in polish) and it works perfect (kernel is already compiled with necessary patches.
I guess you have one gateway but two different IPs to balance? This is a problem cause (i guess) Linux Kernel doesn't accept same gateway on the different interfaces. I've never resolved problem to do this on one router, but there is a hack. Just use simple two SOHO routers (with NAT) and load balancer.
It looks like that :
Rout. NAT Router. NAT
Now you have different networks and different gateways and it should works fine.
You can use DMZ on SOHO router to expose your main router to the Internet.