Based on my knowledge, you can go to Canada for upto 30 days if you have your valid H1B and I94. When you leave US, DO NOT give the I-94 to the officials, even if the official ask for it, since by law you don't have to do so.
When you re-enter the US, just show them the H1B and I94. I suppose if you don't have I94 by then, you will have to apply for H1B visa stamp.
