Canada's Borealis Infrastructure and Australia's First State Investments are the leading the group. The sale was launched in September 2013.
Fortum is also exploring selling its distribution grids in Norway and Sweden, according to reports.
The Finnish grid is worth some $447.7 million in sales, and covers about 20 percent of the country's distribution. Analysts have valued Finland's T&D network at about $12.4 billion, according to reports.