I had a business trip from DFW to Montreal on May 4 to May 12th.
the following maybe helpful for someone of you.
I was F1, and now H1, only have H1b Approval Notice with new I-94 card attached.
On May 4th, I went to Dallas-FortWorth Airport, the old lady let me turn in my I-94. I told her I don't need turn it in since I would travel inside of Norht America. she didn't understand and consult other guys, they answered "YES, H1b could travel to Canada in 30 days, no need turn in I-94 and visa".
Yesterday, I tried to pass through the Customs. the officer looked at every page of my passport, asked me "where is your working visa?". then I explained it is not necessary to apply for visa. guess he is new or he is too young, so he has to go to ask help from other officers...then let me do the finger print, said "everything is ok!".....
Now I am back to my office