Temps in Sonoma in July could be MUCH higher. You'd better plan on being able withstand 100s. All depends on what fog/heat cycle your wedding happens to fall on.
For you "foreigners," summer weather in the S.F. Bay Area can be downright weird to non-locals. The huge Central Valley bakes in summer sun, causing the all the hot air to rise (included those from the politicians). Cooler air from somewhere needs to rush in. The only break in the Coastal Range of mountains is the Golden Gate.
Thus, cool, moisture-laden (often foggy) air from the Pacific Ocean floods in through the Gate and spreads eastward towards the valley, cooling everything down. Sometimes, the prevailing winds are headed out to sea and the whole area bakes. However, this can only last a maximum of three days before "God's air conditioner" kicks in and the fog comes screaming back in.
One day it can be in the 100s and the next in the 70s. So, like a good Boy Scout, you'll need to be prepared.