He will have monthly or quarterly brokerage statements (ether mailed to him or online).
The statements will show stocks held and traded in Canadian Funds (Canadian Account) and stocks held and traded in US funds (US Account).
It’s only the stocks denominated in US dollars, or the US side of the account that need to be reported. If the brokerage doesn’t provide a nice breakdown for T1135 purposes the monthly statements are your next best option.