Yes.
H1B has no effect on entry requirements for Canada. You will need a visa if someone from your country of origin requires a visa.
Yes you need visa
Yes
You need visa
You need a visa even for transit
Not sure about entering Canada, but returning back can be done without needing a new visa stamping: https://travel.state.gov/content/travel/en/us-visas/visa-information-resources/visa-expiration-date/auto-revalidate.html Read this - take a printout and go. You can enter back to US without a valid visa stamping but with an extension as long as you have not visited any other country within 30 days. Important: read through the document and verify you qualify.
It's a different country. Why would it matter if you have an American visa?
It does matter in a few countries. You could get visa on arrival in UAE, certain Caribbean countries if you have a valid US visa. So yes, you could have easier visa privileges in some countries if you have a valid US visa. Research and then speak rather than just slamming people about topics you don’t have adequate info about.
You can go to Mexico too if you have a USA visa. And you can go to Singapore if you have a Canadian visa. Get a Canadian visa.