I don’t know what sort of timelines the US embassies have in India in terms of wait times to get a visa appointment so I can’t comment on the feasibility in terms of getting a US visa.
Answers to your questions -
2. There is no hard quarantine requirement anywhere in America. Some states recommend that people quarantine but it’s just a recommendation.
3. You don’t need an international DL (there’s no such thing as an international DL), you can get an IDP which is a translation of your drivers license in multiple languages from your issuing RTO but if your license is in English, then that’s not strictly required. However if you’re not familiar with driving on the “other” side, then I wouldn’t recommend taking that trip via a rental car anyway. If you’re familiar then getting a rental car (with a one way drop off is easy enough at the airport, it’s definitely more expensive than returning the car at the same place).
4. I don’t know if Cabs are considered essential service so you may not be able to find a Cabbie willing to take you across. My recommendation is that you fly from JFK/EWR to Buffalo NY or the Niagara Falls International Airport. From there take a local cab and have them drop you off at the Rainbow Bridge, you can then walk across the bridge (it’s only a couple of hundred metres of walking). But before you do this please call the bridges commission to confirm that the pedestrian walkway is open. The border is closed for non essential travel, but multiple people have completed their immigration landings so I don’t see that as being a problem for you.
My recommendation if you were able to get a visa and wanted to go through with this would be to first fly to Buffalo or Niagara Falls and then if possible take a 1 way rental car. Walking across the bridge seems iffy, theoretically it should work but you don’t really want to be stranded on foot. Drop your rental car off in a no-contact manner at a location near your AirBnB or Hotel in Canada.
You could absolutely wait and have your COPR extended but at this time there’s no idea of how long this is going to be, it could be later in this year or next year and I don’t fault you at all for trying to get this done and starting your new life in Canada. There are numerous people who’ve been stuck in limbo for more than a year.
All the very best!