Ask the seller.
Most will happily package the items together and discount the postage cost.
But this is voluntary.
Some will combine the items in one shipment, but will not discount. This is stupid bad customer relations.
Ask the seller BEFORE bidding for a quote on the items to Canada. GIve him the item numbers you want to bid on.
I sell books, and while most of the time I can both combine and discount, I have more than once found that the cheapest delivery will be in multiple packages. Depends on service, measurements and weight.