Genstar is planning an all-cash bid for Imasco.

Imasco Ltd. plans to proceed with an all-cash offer of $1.69 billion for Genstar Corp. instead of an alternative proposal of cash and securities, the companies said. Genstar is a Canadian building materials and financial-services concern whose main office is in San Francisco. Imasco, based in Montreal, owns Canada’s leading cigarette maker, drugstores and restaurants.