Unfortunately, the battle was already fought and lost. The US Supreme Court has already ruled the federal government can enforce its laws against marijuana regardless of state law. I think Clarence Thomas has it right (he argued that medical marijuana had nothing to do with interstate commerce).
If California bars all CA police officers for providing any cooperation with federal authorities on this matter, regardless of any "grant" the feds might offer to buy cooperation, then the feds will have a hard time enforcing the law. If California combines that with a vigorous "jury nullification" education program, then the feds will really be in trouble.