If you are deer scouting what kind of bunny's will you be running into...snowshoes or cottontails? Both? what kind of shots will you get? If you will be deer scouting in classic bunny territory then i would go with a 20 guage if you have one, if you don't have a 20 then the 12 gauge will be fine with any shot from six's to eight's. I prefer six.
But if you will be scouting in closer tighter cover, like cedar swamps, you might be better of with a .22. I love the sneak and peek game with snowshoes in the cedar swamps. They take off...go a little ways and then stop and freeze. If you can follow them with you eyes you can pick out their little black eye against the snow. I carry an old Marlin bolt action .22 with a 7 shot magazine and a fixed power 4X on top. Cottontails usually go farther and are not found in good numbers where I deer hunt.