Liam here from Shopify - thank you for your question :)
Great to see you are investigating different methods for distributing your products to your customers. There are a number of ways to ship from China to the US and Canada which have varying degrees of speed and cost. The cheapest form of shipping would be regular post, but this can have a very slow delivery time- 2 to 5 weeks from the product to arrive.
Another option, and one which is very popular with our merchants would be to use an express courier such as DHL/FedEx/UPS/TNT to deliver your products. With express courier services, you get every package hand-delivered anywhere in the world within 1 week. However this could be significantly more expensive than regular post. To get an idea of these costs you can request a quote from Fedex here for shipping from China to an American address.
Hope this helps, if you have any other questions, just let me know!
Your question is a little bit conflict. The courier service is the fastest way shipping from China but is is the most expensive way.
If you shipping frequently from China, the shipping fee can be cheaper, all you need is to find a forwarder shipping agent in China to help combine packages to save first weight and ship via UPS or FedEx, I guess that's the most affordable and fastest way to ship from China to US and CA.
As Liam has mentioned, the cheapest form of shipping would be the regular post, but this can have a very slow delivery time like 2 to 5 weeks for the product to deliver. The best option would be to use FedEx, which provides the best service. Also, FedEx handles the customs and insurance much better than other carriers.
Since Shopify doesn't support direct shipping with FedEx, you can use the FedEx Rates, Labels & Tracking app which would help you show real time FedEx rates at checkout, print FedEx labels and also handle FedEx tracking.
Cheapest shipping services are the ones with are run by government. So if you have China post sending shipments to these countries, then you should opt for it. Also, if you are planning to use private couriers for shipping, then UPS would be the right choice as they have access to majority of serviceable areas. Also, if you are using multiple carriers like UPS, FedEx, DHL, you can use try multi carrier shipping label app that will further cut down your cost of shipping as you won't have to opt for multiple solutions.