Why Canadian industry would not remove Narvik's value

Would greater British investment in Canadian foundries and shipyards prevent the Battle of Narvik?

No; Narvik's strategic value came chiefly from denying Swedish high-grade ore to Germany, not from British dependence on it.

Britain already produced and imported iron from elsewhere, and expanded Canadian foundries would strengthen that base further. Narvik still mattered because Germany depended on high-quality Swedish ore: stopping the traffic denied an important input to German industry, while diverting it to Britain created an additional gain.