This depends on how much out of level your base cabinets are. If they are way off (3/4" or more) then you will need to unfasten all of them and install them level. Find the high point along the wall. Start here. Then make a level mark 34 1/2" from this point along all walls getting base cabinets. You can screw a 2X4 cleat along the back wall to support the base cabinets. Mark this line 30" down from your level reference line for the top of the cleat. Then just shim the fronts to level the back to front plain. If you are not that far out of level the granite top can be shimmed level and the gap caulked.
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!