There's an old saying "You can have it good. You can have it cheap. You can have it fast. But you can only pick two."
This may not be an item that should be shipped by mail, unless the seller/shipper is experienced with packing fragile products. KJJ or CL may be your best venues.
Having said that, I understand that UPS will pack items for you, and offer insurance on safe arrival. If you do your own packing, insurance against damage becomes more expensive or just not available.
UPS is very good for domestic shipping.
For foreign shipping, make that US destinations, if you expect to sell for over $200, your buyer will be paying duty and local sales taxes, plus a service fee to UPS if you use the cheapest Surface rate. And unless the computer was manufactured in the USA, it is subject to duty.
Your US buyer will be furious if you allow this. So plan to ship to the USA by the more expensive Express service which includes duty, tax and service fee. Don't explain this to your customer. Just give the cost. Either he will pay it or he won't.
If you use Canada Post, keep in mind that your parcel will be on conveyor belts. The drop from one belt to the next may be upwards of two feet. The parcel that drops on yours may weigh some 50 pounds. Pack accordingly.
Some sales are not worth having.