Analyze the relationship between 'ATCO' and 'Canadian Utilities' within the context of the input sentence.
Options: legal form, operator, stock exchange, subsidiary

In June, we announced that the LUMA Energy, a joint venture between Quanta and Canadian Utilities Limited and ATCO company, was selected by the Puerto Rico Public-Private Partnership Authority for a 15-year operation and maintenance agreement with the Puerto Rico Electric Power Authority, or PREPA, to operate, maintain and modernize PREPA’s more than 18,000-mile electric transmission and distribution system in Puerto Rico.
subsidiary