Can the visitors to U.S also visit Canada and come back to U.S?

[sfolenaa]

I am a citizen of the U.S and I have couple of family members (citizen of Republic of Korea) coming to visit with ESTA visa. Can they visit Canada and come back to U.S? Some people say they can enter Canada but would have to go straight back to Korea once they are done touring. They want to have a trip from Korea to U.S to Canada and back to U.S and to Korea. I'm wondering if thats possible.

 

[Jalex23]

I am a citizen of the U.S and I have couple of family members (citizen of Republic of Korea) coming to visit with ESTA visa. Can they visit Canada and come back to U.S? Some people say they can enter Canada but would have to go straight back to Korea once they are done touring. They want to have a trip from Korea to U.S to Canada and back to U.S and to Korea. I'm wondering if thats possible.

They need an eTA.

http://www.cic.gc.ca/english/visit/eta-start.asp?lnktrk=eta_required