There's been alot of debate going on about this at my house.I always pronounced it as cay-vee also, but then I was led to believe it was pronounced as ca-vee.
I always thought it was ca-vee too. But this is because in Dutch, they pronounce it ca-via. So I just assumed the A sound was the same in English. I didn't even know they were called "cavy" until I got my first one. Until then I thought their proper name in English was guinea pig.
Yup,You pronounce it as Cay-vee. I'm definetly sure now,I've seen it pronounced that way many times in many books.It's definetly pronounced as Cay-vee,not any other way.