You can visit Canada or Mexico for up to 30 days without having to renew your visa, as long as your I-94 is still in status, under automatic revalidation. (Note that students on F and J visas can also visit certain Caribbean islands under this program, but H visa holders can only visit Canada and Mexico.)
You should bring a copy of your I-94 with you, as it will speed things up with Customs and Border Protection, and the airline will need to see it in order to board you if you are flying.
The complete rules for automatic revalidation are available in CBP's Automatic Revalidation Fact Sheet.
Also note that this does not exempt you from the requirement to obtain a visa for Canada, if Canada requires a visa from people of your nationality.
Finally, a caveat: Automatic revalidation is not available if you are traveling on a passport from Iran, Sudan or Syria. In this case, you must either remain in the US, or renew your visa while outside the US.