What does the seller's listing say, - is a combined shipping rate offered? Sometimes it is done automatically at checkout. Other times the seller sends an invoice when you're done shopping.
Canada does not have the shopping cart feature. If the items are the 'free shipping but immediate payment' type, you can add the lot into a cart if you go to ebay.com. That way you can pay for all your items at once using the US checkout.
Otherwise it is certainly possible to buy multiples from the Canadian site. If the seller's listings tell about combined shipping, you can send a note or use the Request total link when you're done. If no mention is made of combined shipping, then use the Ask a question link to find out about it.
