If you go to Canada by air, the clerk at the airline check-in counter will check your Canadian visa before giving you the boarding pass. They do not retain your I-94 card if your trip destination is in Canada.
You can re-enter U.S. with Automatic Visa Revalidation provided that you meet the following requirement:
You stayed in Canada (or Mexico) only, for less than 30 days. You have proof for your current and legal immigration status in the U.S. You did not apply for any visa at the U.S. consulate in Canada (or Mexico).
If you go to Canada by car, it will be even easier.
Make sure that you bring all the documents that show your current H1-B status.