I don't know which listing you are referring to, so cannot give you any clear direction on the ordering part. Most listings that allow this are set up so that multi-quantity/size/colour ordering is easy. Since you have sent a message to the seller, wait a few days for a response - there may be a time difference, they may be a one-person operation and be at work or otherwise busy. If you do not get an answer, this may give you a clue as to how this seller may handle any problems that may arise with the purchase, and that might steer you to another supplier who is more responsive. If you get an answer, by sure you understand the total price for shirts and shipping before you commit to buy.
However, the bigger concern is that you mention huge costs for shipping to Canada. A T-shirt is thin and lightweight and easy to ship in a poly mailer. Is this listing using the GSP? Here is how to identify GSP items - below the price information, does it state :
No additional import charges at delivery!
This item will be shipped through the Global Shipping Program and includes international tracking. Learn more
Does it show shipping as International Priority Shipping to Canada?
Is there a line below this with Import Charges?
For GSP listings, the seller is actually shipping domestically to a distribution centre in Erlanger Kentucky. From there, Pitney-Bowes takes over, preparing the customs information and consolidating shipments. They add their shipping & import charge to the seller's total price. The US seller is often not aware that the final destination is Canada, since for him it is a domestic transaction. S/he may also not know how the listing appears to Canadians shopping on ebay.ca. They may not answer your inquiry since they may think they do not ship to Canada - many US sellers are unaware that they are enrolled in the GSP program.
I have heard that it is not possible to combine GSP shipments, that is, you may not get a shipping discount. The import charges will not decrease, since these are made up of import taxes (equal to GST/HST), and duties (most T-shirts come from China or other countries and may be subject to duty) plus the fee for preparation charged by P-B - about $5.00 according to other posters. Even if the T-shirts are made in the USA, the seller may not declare this on the package , leading P-B to open and confirm, then repack, which they apparently are not very good at doing.
I notice that out of the 8 feedback that you have left, you have given 4 negatives. If you have had such an unsatisfactory experience on eBay, why would you want to buy a multi-item order with high shipping costs from an unresponsive seller? Could you possibly be setting yourself up for another unsatisfactory experience?
And as an aside, shipping costs are what they are - it is expensive to ship from Canada to USA, within Canada, etc - costs for US sellers have increased as well - this is a business expense, nothing to do with being good neighbours.
