Alcoa Inc. (AA) is offering to buy Canadian aluminum rival Alcan Inc. for cash and stock worth nearly $27 billion after failing to reach a negotiated deal.

Alcoa said the proposed deal would create a premier diversified global aluminum company which could grow faster than the companies could on their own.

The company is offering a combination of cash and stock that it said was worth $73.25 for each Alcan share, a 20 percent premium to Alcan's closing price Friday of $61.03.

The bid includes $58.60 a share in cash and 0.4108 of an Alcoa share for each shares of Montreal-based Alcan.

With about 367 million shares outstanding, that values Alcan at nearly $27 billion. Alcoa said debt being assumed would boost the total value of the deal to $33 billion.

Alcoa said in announcing the offer on Monday that it had made an offer to Alcan last fall, and decided to take its offer directly to shareholders due to the companies' inability to reach a negotiated deal.

Alcoa expects to begin its offer on Tuesday.