That is possible at BGP… your home internet providers not support that at 99% at your service plan.
It’s material from MTCINE course.
For general ISP you can try few policy of doing LoadBalance, check the presentation of Tomas Kirnak at point 2 this post http://forum.mikrotik.com/t/moving-from-fail-over-to-using-both-wans/143145/2 .
TL;DR nth, PBR, PCC, BandwidthMonitor - this ways.