Everything is in Canadian dollars
Your Canadian return is in CAD, so every US-dollar transaction must be converted. You buy at the exchange rate on the purchase date and sell at the rate on the sale date — using the rates that applied then, not one annual average and not today’s rate. The Bank of Canada daily rate is an accepted source.
US dividends and withholding tax
US dividends are fully taxable in Canada (no dividend tax credit — that’s for Canadian dividends). The US typically withholds 15% under the treaty in a non-registered account, and you can usually claim a foreign tax credit to avoid double taxation. In an RRSP, US withholding on US dividends is generally exempt by treaty; in a TFSA it’s usually not recoverable.
Cost base in CAD
Your ACB for US shares is tracked in Canadian dollars, converted at each purchase. Pool identical US shares just like Canadian ones. Doing this by hand means a rate lookup for every buy, sell, and reinvested dividend — the tedium that makes US holdings error-prone at tax time.
A note on US estate tax
Large holdings of US-situs assets (including US-listed stocks) can expose a Canadian to US estate tax on death above certain thresholds. It’s beyond income-tax filing, but worth knowing if your US holdings are substantial — a reason to get cross-border advice.