The Nordic country’s admission to NATO last year drew threats of “counter measures” from its vast Russian neighbor.
In December, Finland closed its entire border with Russia to passenger traffic in response to a surge in migrants trying to cross. Moscow denied Finnish charges it was sending them there.
All nine candidates are promising a tough stance toward Russia if elected president, a role that leads on foreign and security policy in close cooperation with the government and represents the country at NATO meetings, while also acting as a Commander-in-Chief of the Finnish Defense Forces.
The center-right National Coalition’s Alexander Stubb has emerged as the frontrunner, with recent polls giving him 22-27% support in a first round, just ahead of liberal Green Party member Pekka Haavisto, who polled at 20-23%.
The nationalist Finns Party’s Jussi Halla-aho is not far behind Haavisto, at 15-18%.
Bank of Finland Governor Olli Rehn and Social Democrat European Union Commissioner Jutta Urpilainen are among the other six candidates from across the political spectrum.
If no one gets more than 50% of the votes cast on Sunday, a runoff will be held between the first and second candidates.
Partial results are expected shortly after polls close at 1800 GMT and the competitors for the probable second round should be clear by 2030 GMT unless the results are very close.
The new president will replace 75-year-old incumbent Sauli Niinisto who is required to step down after two six-year terms in office.
He earned the nickname “the Putin Whisperer” during his tenure for his role in maintaining close ties with Russia, which had long been a key role for Finnish presidents.