Channel sales is wherein the product reaches the end user 
from the producer end, through the typical distribution 
channel. Example: 1) Producer--Distributor--Retailer--
Customer
2) Producer--Agent--Distributor--reatailer--customer
3) Producer--Sales Personell--customer

Corporate Sales is wherein corporate houses are directly 
approached by the sales team. 
(Note: To me Corporate sales is one of the channels is only)

hope this helps