When using fresh corn in place of canned or frozed, should I cook the corn first?
Good question! Corn is very versatile. I've found that fresh and frozen whole kernel corn are very interchangeable when used in casseroles. Most casseroles cook long enough that you could use either without making any adjustments.

However, canned corn is a different animal. Because it is more processed I would use it in recipes that call for it but I would not consider it a substitute for fresh or frozen.