three main methods
Round Robin - means taking turns for next session by the two WAN
Least Load - router assesses load and pushed next session to least loaded interface (not sure if hex looks at up down or both)?
Fail-over (not really load balance but simply use WAN2 only if WAN1 is not available).
Round Robin can also be weighted, so as to even out the load balance based on throughput capacity.
For example you have a 60:20 capacity difference 3:1 so to speak.
So it would be best to have 3 sessions go to WAN1 and then the next session go to WAN2 for example.
So asking for load balancing needs more clarification.
What kind of approach is required?