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I am assuming that you guys are not Canadian citizens, since you have a US visa and are talking about getting a US visa for your family member, and Canadian citizens do not need US visas to visit the US.
If your family member has a passport from a Visa Waiver Program country, they should get an ESTA to enter the US on the Visa Waiver Program.
Otherwise, your family member should get either a C1 transit visa or a B2 visitor visa to enter the US for transit. A visitor visa can be used for transit, and since they are going to the trouble of applying for a visa anyway, they might as well apply for a visitor visa, so that it can be used for visits later, unless for some reason they are likely to be denied a visitor visa.