Heat oven to 350°F.
Combine garlic, remaining rosemary and half the oil in small bowl. Remove giblets and visible fat from hens; wash and pat dry. Season hens, inside and out, with salt and pepper. Run finger under skin of breast to separate from meat. Rub garlic-rosemary mixture under skin; place sage leaf under skin on each breast half, if using. Rub outside of hens with remaining oil. Place hens, breast side down, in roasting pan. (Can be done in the afternoon of the dinner. Refrigerate, covered.)
Roast in 350°F oven for 20 minutes. Turn the hens over, breast side up. Roast 30 to 40 minutes or until instant-read thermometer inserted into thickest part of thigh without touching bone registers 170°F. Remove hens; let rest for 5 minutes.
Meanwhile, pour off excess fat from roasting pan. Add small amount of liquid from cherries to roasting pan. Place pan over medium heat; scrape up any browned bits from bottom of pan. Add cherries; heat through. Remove pan from heat.
Split hens in half lengthwise with kitchen shears, cutting on either side of backbone and down center of breast. Serve half a hen per person, spooning cherries over each portion.