This might have been discussed somewhere, but I could not find it. I really need help on this. Following the advice here, I booked the frame work itinerary for March, and then call United to change the flight to July. (because it didn't price online for the July itinerary that requires more segments due to the award ticket availability.)

IAD->SFO->HNL (stopover)
HNL->GUM->MNL->SIN (destination, open jaw)
CAN->NRT->SEA->CLE->IAD

The agent told me that I had 9 segments and the max number of segments was 8. Is this true? Where is this rule specified?