You're right. There is nothing in the bill that requires the work location to be in Canada, so yes, it's possible that the deduction could be claimed in respect of someone who is commuting to the U.S. for work.
In those circumstances, it would really depend on all the facts as to whether that person would be subject or not to Canadian tax on that income. The deduction is not limited to just income from that particular employment. It's a general deduction from income, so yes, it's conceivable that someone could be working in the U.S., potentially paying U.S. tax, depending on the facts on that income, and claiming a deduction in Canada.