How does that work? Amazon will give you a code, you redeem the code on nintendo eshop?
I wouldn't recommend that given the actual implementation of region restrictions on the switch is still not clear. If you buy from Amazon, you will surely get a code for the US eshop. But what if your account is SG or Canada, can you redeem the code on your SG account? And what if the actual Botw game we get in SG is the UK version (many games apparently are cheaper in UK so local game shops tend to bring in those), will the US expansion work on the UK game? If I have SG console, using Canada account, playing UK game, and from within the game's menu it links me to eshop to purchase the expansion... which country's eshop will that be? Will they accept SG credit card?
I know I know, there is no region restriction. That's not saying a lot without going into the details. All it means is that you can buy a UK game and play on your SG console, but it doesn't tell you whether you need to use a UK account to play the UK game, for example. We don't even know whether one Switch allows multiple account, of different regions, and if so how games/DLCs can be shared among them. Expansion/DLC compatibility across regions is yet unknown. Best to hold off buying expansion until more is revealed.