Totally possible. You want to do your connection to the NAS at the ESX level. We have multiple remote sites, and we use NAS devices connected through iscsi for each one of them. Most NAS devices provide documentation on all the how-tos, so I'd suggest starting there.
Etherchannel and iSCSI is just asking for trouble, and you will be limiting your iSCSI design, here some good reading material. But as always, consult your storage vendor documentation.