I can them after I roast, peel, seed, and chop them. Freezing is way easier if you have the space, roast them first, then pack into freezer bags just like they are. When it's time to use them, defrost, and the peel slips right off. Everybody I know around here makes chile rellenos with Anaheim chiles, any other chile is a sacrilege to me. Jalapenos make good "poppers", stuffed with cheese, coated and fried.