Do you mean from the same seller or different sellers? If the same seller, - see what the listings say. If the seller offers a combined rate for multiple purchases there should be some mention of this in the listing. The discount will either be applied at checkout, or you send an email to the seller when you are finished shopping. You then wait for the invoice with the reduced shipping fee.
If it is for different sellers, you can click to buy each item and then when you're done, provided they are all in the same currency, you click to pay one of them and the lot appears at the checkout, -- you pay once for all of them. Obvously there will be no 'discount' when buying from different sellers.
If some of the items are "immediate payment required", you can either pay them from ebay Canada one by one, or go to the US ebay.com, sign in there, and use their shopping cart feature. Canada does not yet have the shopping cart feature for some reason, but I'm sure it will be here soon.
Happy shopping! 🙂
