According to the Oxford English Dictionary, you should indeed roll your L when you say carillon — if you pronounce the L at all. Carillon is originally a French word, and the French (who dislike letters of all kinds) pronounce it kuh-REE-yaw, nasalizing the last syllable and dropping the N. But we English speakers like to pronounce all our letters (damn right, we do!), so in English, it’s more often said KAR-ill-yon or kuh-RILL-yun. It’s also occasionally pronounced “bell-tower,” but never KAR-ill-on.