I personally agree with all 3 bullets above. If you are not US tax resident that's one thing, but if you are US citizen that's a total different story. The US Interactive Brokers told me if I am US citizen with US account with them and move to Canada - all I have to do is just to change an address with them, that's it, no changes as far as trading. My IRA is with Vanguard and Fidelity - for them looks like is better to keep US address even if I moved to Canada. Again- this is for US citizen living in Canada.Not sure about this. Most Canadian brokerages e.g. Questrade, Interactive brokers let you trade in world markets e.g. USA.
You can also hold currency in USD. So you lose nothing in terms of choice.
Of course, you don't have Robinhood. But I'm not sure you'd want that anyway.
By the way, are Canadian brokerages commission free like all major US brokerages? Can I get no load mutual fuinds like Vanguard Wellington Fund (VWENX) with expense ratio 0.17% or Vanguard Wellesley Fund (VWIAX) with expense ratio 0.16%?