EIGRP has a feature that will allow the load of an interface to be included in the metric, and a feature to allow unequal cost load balancing, but both of these are off as default.
To turn on load use:
router eigrp
metric weights 0 1 1 1 0 0
Default would be
metric weights 0 1 0 1 0 0
That would then include the load in the metric calculation.
To allow uneven cost load balancing:
router eigrp
variance 2
will allow the high meteric used to be dounle the low metric.
Having said this, having interfaces with effectively variable metrics where the metric can influence the metric (I'll come back to that) may not be the most stable idea.
As I say about metric influencing metric just consider this.
You have simply a pair or routers, with a pair of matching links between them, running eigrp across the links. Before there is any traffic, the metric for both is equal. Due to the nature of the traffic, one link gets a little more traffic, so eigrp adjusts the metric to favour the less loaded link. Traffic not starts to favour the previously light link, so that now becomes the heavier used link, so EIGRP again adjusts the metrics...
