Sure they wouldn't stick out here, but I don't think it's that easy to come to Canada - how easy is it to get a fake passport? And they'd have to say why they were coming here. Just for vacation? Where are you staying, they may ask the address, and for how long?
You'd think they'd be able to check for any passport combinations that match the three traveling together? Maybe?
Plus then they arrive here and how would they get a job if they needed one? Maybe he had lots saved up if he was living at home, but will it last forever? It's 2024, not many places will pay you cash under the table. They wouldn't be able to direct deposit into a US bank account, only Canadian etc.