If it’s into Canada, I don’t think you have that option. If it’s into the US, then yeah, they have to let you enter, so I assume refusing face scans is allowed. They can certainly detain you, but you have rights. IANAL though, and YMMV depending on the color of your skin and/or accent, unfortunately.
Does this also apply to the face scans they ask U.S. citizens to do when passing the Canadian border?
If it’s into Canada, I don’t think you have that option. If it’s into the US, then yeah, they have to let you enter, so I assume refusing face scans is allowed. They can certainly detain you, but you have rights. IANAL though, and YMMV depending on the color of your skin and/or accent, unfortunately.