If Mr Peters wins, National will be one MP down and no longer able to rely on Mr Seymour's support alone to pass legislation.
The impact of Mr Seymour's gesture is likely to be minimal - Act got just 162 votes in Northland in 2014. However, Focus New Zealand candidate Joe Carr, who has stronger local support, said his party was also likely to steer supporters to vote.
It was undecided whether it would be for Peters or Osborne but he would rate them on their policies for Northland.
Mr Carr, a Northland regional councillor and farmer, polled 5 per cent in the recent One News Colmar Brunton poll. Mr Carr said one concern was the allocation of roading funding, which he called "an urban apartheid system" because the regions missed out.
Others included stabilising the New Zealand dollar and foreign ownership of farmland - hints Mr Peters could get the nod. He questioned National's campaign promises to upgrade 10 bridges, saying it was not new funding and would jeopardise other projects.
Labour leader Andrew Little said Act and Mr Seymour were "the political masters of electoral deals and political schmoozing" but if National was relying on that deal for salvation it was in trouble. He denied his message to Labour supporters to vote for Mr Peters was a similar deal. "There is no deal. What there is is an acceptance of the reality of the situation that two polls tell a very similar story.
"It is up to the voters of Northland to decide if they want to exercise their vote in a way that sends a message to the Government that they don't want to be overlooked anymore."