You do need Canada Visa to go to Canada, but

you don't need US visa to come back as long as you hold valid I-94 (for H-1). If you have AP, that also can be used to reenter US, but not necessary.

For Canada visa application, check Canadian Embassy website. All the necessary documents are list.

BTW, don't think you have Canada visa you can get into Canada. The border office still can refuse you to enter. The most important think is you have to bring the evidence that after staying in Canada, you will leave. Such evidence include air ticket or US visa (expired one is ok). Good luck!