Somewhere on the listing, probably the right hand side, there is a link Contact Seller.
Let her know what you want to order.
If the seller is in the USA or UK, she may be signed up for the Global Shipping Program*. (This would be stupid if the buttons are under $50 a pack, but ....) In this case, she will NOT be able to combine and discount shipping.
However, you could ask her to make a listing just for you with the seven packets you want and corrected shipping that does not involve the GSP.
You want USPS/Royal Mail shipping. Long story....
If there is no GSP involved, use the Contact Seller to ask about shipping cost to Canada. Most sellers will be happy to adjust it.
If there is Free Shipping, just order all seven at once, eBay should automatically combine the invoice.
While buying on eBay is pretty simple, shipping costs can be hard to understand. It is always useful to confirm that the seller does ship to Canada and what the shipping cost will be.
*The GSP does not show up when you are browsing with a mobile phone. Actually I believe it only turns up, with mobile devices, when you get to the point of paying. And that's one of the minor flaws.
