As a former Revenue Manager, I can say that most hotels won't enter into rate negotiations unless you're talking about hundreds of room nights per year. From the hotel perspective, the time it takes for a sales person to haggle would better spent calling on companies that can produce those hundreds of room nights.

As a brand, there's no incentive for Marriott to give any discount on the rate. They already incentives for frequent guests via the Marriott Rewards Program.

Fortunately, for the OP, smaller limited-service properties that rarely sell out might be willing to negotiate. I grew up in the Inland Empire and still have family in that area. The economy is still depressed. That means it's possible that a small property in Ontario might be willing to offer something in exchange for a few dozen guaranteed room nights.

As other people wrote, any negotiation would be directly with the hotel. Ask for the Sales Manager (who may also be the General Manager).