If you have Canadian permanent residency or have a Canadian visa, you can live and work in Canada. If you are a visa exempt national, you can visit Usa without a visa else you need a visa to enter.
You cannot work in the USA if you immigrate to Canada. You are perfectly free to visit the USA, but you will be subject to the same immigration checks as everyone else, your Canadian PR does not grant you special privileges.
You are confusing PR with citizenship. Like others said with PR you have to go through visa if you are not a visa exempt national and your duration of stay depends on the type of visa.