WordNet sense 1 (pleasantly (even unrealistically) optimistic):

upbeat, pollyannaish

WordNet sense 2 (expecting the best in this best of all possible worlds):

optimistic

WordNet sense 3 (having a cheerful, lively, and self-confident air):

chipper, debonair, jaunty

WordNet sense 4 (bright and pleasant; promoting a feeling of cheer):

cheery, sunny

WordNet sense 5 (bringing cheer or gladness):

cheering

WordNet sense 6 (characterized by liveliness and lightheartedness):

buoyant, perky, chirpy

WordNet sense 7 (carefree and happy and lighthearted):

blithe, blithesome, lighthearted, light-hearted, lightsome

WordNet sense 8 (smiling with happiness or optimism):

smiling

WordNet sense 9 (cheerful and bright):

glad