Rio Tinto has picked McCarthy Tétrault as its leading Canadian counsel, with Alcan opting for Ogilvy Renault.
Rio Tinto's bid for Alcan comes weeks after mining competitor Alcoa made a hostile $33bn (£16.25bn) approach for the same target. Alcoa's advisers are Stikeman Elliot in Canada and Skadden Arps Slate Meagher & Flom in the US.
Clifford Chance's global head of banking Mark Campbell is advising banks Deutsche Bank, RBS, Credit Suisse and Societe Generale.
The new group, Rio Tinto Alcan, will have its headquarters in Montreal.