There are a number of ways you can pay your GST balance owing if you are an amazon.ca seller.  Depending on the amount of GST you might owe, these solutions could be better or worse depending on the amounts and fees.

1. If you have a Canadian based bank account, most major banks will have a tax payment option available where you can pay your GST amounts owing for a very small fee.
2. You can pay by wire transfer.  https://www.canada.ca/en/revenue-agency/services/about-canada-revenue-agency-cra/pay-wire-transfer-non-residents.html
3. You can pay by credit card using https://www.paysimply.ca/cra/ which will allow you to use your home currency credit card and easily pay your taxes.   There is a small fee involved. Please ensure you select Business Taxes > Enter your business number with RT0001 ending > Select Payment on Filing (GST/HST NETFILE).
4. Another alternative is to open a virtual account with OFX.com.  This allows you to get your amazon payments left in Canadian dollars and exchanged into US or other currency at a better rate than most banks.  My personal rep Amelie.Deschenes@ofx.com is great and can get you set up.  You can also then set up additional currency accounts across the world and have all markets paid into one.