Can I hold US dollars and buy US stocks (with US Dollars) without FX commissions using a Canadian brokerage account?

May be moving to Canada next month, so I had some questions.

I would like to transfer my US dollars to a Canadian brokerage account — from what I’ve read IB or Questrade are the best options.

However, assuming I can hold US dollars in my brokerage account, I would hate to pay foreign exchange fees every time I acquire a US stock, say, AAPL or BRK’B.

I understand the answer will depend on whether my brokerage account is a margin account, TFSA or RRSP. I would be interested, if possible, in knowing the answer to my question for all three cases.

Thank you.