Case 1: Can I get Canada PR (already having a tourist visa)?
PR visa doesn’t relate to a tourist visa. A tourist visa is just a period of your stay in Canada.
Case 2: Can I get Canada PR (already having a tourist visa) if my sibling is a citizen of Canada?
You cannot get PR with a Tourist visa even though your sibling is a citizen of Canada. But, if you have siblings as a Canadian, then you can have to increase your Points for a PR visa.
Case 3: If I get a job offer letter from Canada, how much will it help for PR?
If you have a Job letter from Canada, it is alone more than enough to get a PR visa for Canada. But you have to submit necessary documents for your PR validation. You must get necessary score points and should have police clearance, etc.,
To know necessary documents for Canada PR visa and to get PR at any condition, get help from the registered Canadian consultants.