I'm a daytrader of US stocks, but if I trade stocks on the toronto, london, or tokyo stock exchange, can I still simply use mark-to-market accounting and file taxes the same way as if the income was from all US stocks?
I think you can for all of them. Well I know you can for Canada. Only consideration would be FX and transaction taxes in London. I have never traded london stocks so I do not know if you can include the tax in your cost basis when you trade from outside the UK.