We went to US Consulate, Ottawa and got my wife's TD visa stamped in her passport. Very straightforward, took just 2 days to get the stamping done.
Before travelling back to US, detached the new I-94s that came with the 797 A approval notice (bottom portion) and stapled it to the old I-94 (valid until Jan 30th 2018) that is there in the passport.
On Jan 27th, crossed the border at Ambassador bridge, officer just asked one question, How long you are going stay in the US during this trip? I replied, I got my TN status extension until Jan 2021. He gave the passports back and said have a great day! that's it.
@ nelson - Now I have my old and new I-94s in the passports, if I am guessing it correct, when I cross the border in future, I should simply remove the old I-94 and keep only the new I-94 that came with the approval notice? Appreciate if you could share your thoughts. Thanks.
For more info please visit this link: http://forums.immigration.com/threads/uscis-i129-for-first-time-tn-appli...