From reading thru their international shipping FAQ it appears that they do not offer free shipping on any international orders and all customs, importation, etc fees fall to the buyer.

With that in mind it probably works best for your case to stock your bins in a single order of the common sizes of screws, nuts, and specialty fasteners that you regularly need so that you can limit the fees you have to pay instead of making a new order every time you spin up a new project.

They regularly send email alerts to special pricing events. I don't know how that plays out for someone in Canada though. The shipping costs on my end are fairly low since I tend to order a few things at a time and the contents of one order easily fit into a standard USPS mailer or a small padded envelope.

Another thing that may work for you is Fastenal [0] since they operate in Canada and offer metric fasteners.

[0] https://www.fastenal.ca/product/Fasteners/Bolts?fsi=1&catego...