https://www.microsoftstore.com/store/msca/en_CA/pdp/Halo-5-Guardians-for-Xbox-One/productID.1448262000?tduid=(d186b73fd9207d7f8ae0e2e96dbe6a35)(240780)(2316686)(CAqD7bLWUPI-1Zxlh1ZaN.6yw8b_u4ly9g)()

For some reason the Canadian version is on sale but American isn't. But I assume Americans can use the code just fine

Is Xbox live region locked? I donot really know.

I know Canadians can't buy American PSN cards and use them.

The xbox one is region free and you can own currency/ games from multiple regions.
I once bought US currency to get a indie game that was delayed in Canada...
Also won some USA currency cards which added to my US currency, to see/use that currency you must change your console region/language.
Which I did multiple times and asked Microsoft support multiple times and they have no problem with it.
As long as the game is bought in any region it is tied to your account.

My account is Canadian and as you can see I have USD currency on my Microsoft account...hurray for region free