If a principal of a Canadian corp (and is eligible for a TN visa under the professionals list) goes to the US for a week at a time, occasionally, to perform paid work for a US entity (the paid work will be by invoice from the Canadian corp to the US corp), is the best approach to have the US corp sponsor a TN visa and use a 1042-s for the amounts paid for the Canadian individual's work in the US? Would that mean that the US corp withholds 30% for taxes and pays the Canadian corp the balance?