It would be *possible* but would require a fair amount of hand coding to accomplish. There would need to be a column in the cart to determine the seller, then the checkout process would need to be modified to loop through the items in the cart and process each sellers items individually.
We do not have any tutorials that will help you accomplish this, it is not a supported feature of eCart. You would need to be proficient in writing PHP code to successfully accomplish this. perhaps you could get some assistance with this from an experienced member of the community by posting the Job Board.