PREHEAT oven to 350 degrees. Coat a 2-cup casserole dish with nonstick spray.
MIX in a medium bowl the mayonnaise, sour cream and Parmesan. Fold in artichoke hearts. Taste and season with the garlic and onion salt, if needed. Spoon into prepared casserole dish. (At this point, dip can be covered and refrigerated up to 1 day. Add 5 minutes to baking time.)
BAKE in 350 degree oven about 20 to 25 minutes, until mixture just bubbles and browns a bit.
MAKE Garlic Bread Rounds. With a serrated knife, cut French bread into ½-inch slices. In a small bowl, mix butter and garlic. Spread on one side of the bread.
PLACE on baking sheet. Put in oven with casserole for the last 4 or 5 minutes of baking. Serve at once with the hot dip.