Image copyright Getty Images

The 2017 Super Bowl showdown between the New England Patriots and the Atlanta Falcons is days away.

But another battle is being played behind the scenes - and it is bigger than a Budweiser Clydesdale.

The National Football League (NFL) and Canada's telecommunications regulator are locked in a months-long legal and public relations fight over what ads can appear on Canadian TV screens during this Sunday's championship game.

For the first time in some 40 years, Canadian ads will no longer be inserted into US broadcasts of the game.

The change was put in place by Canada's independent broadcast regulator, the Canadian Radio-television and Telecommunications Commission (CRTC), which says that the glitzy US ads are part of the reason football fans tune in to the big game.

In a populist and surprise move, the CRTC mandated that as of 2017, any Canadian broadcaster that owns the rights to the Super Bowl will have to stop subbing Canadian ads over the US commercials on American feeds, a practice called "simultaneous substitution," or simsub.

In previous years, whether a Canadian football fan watched the game on CTV - a Canadian channel - or Fox, for example, they would only see Canadian ads.

The NFL claims this change is an "arbitrary attempt by the CRTC to disadvantage not only the NFL, but Canadian broadcasters and the Canadian creative community as well."

Image copyright Getty Images Image caption The NFL, led by Roger Goodell, is fighting the Canadian regulator's ad decision

Siding with the league is Bell Media, which owns the rights to the Super Bowl in Canada; unions, advertisers, and politicians on both sides of the border, including Florida Senator Marco Rubio.

Both Bell and the NFL have a financial stake in having Canadians watching Canadian ads.

Bell media says they could lose millions because Bell relies on Canadian ad sales to counter the costs of the exclusive license. The NFL stands to lose next time Canadian rights to the game are being negotiated, because they are likely to be sold for less if there are fewer captive viewers for Canadian ads.

The league has been on a lobbying blitz on Parliament Hill, seeking political allies to overturn the new policy.

In December, Sen Rubio, along with Wisconsin Senator Ron Johnson, wrote an open letter to Canada's ambassador in the US, saying the regulator's decision change "sends a troubling signal" about the Canada-US trading relationship.

The NFL recently ramped up the stakes, warning that it had informed "the highest levels of government in both the United States and Canada", including US President Donald Trump, about the broadcast spat.

Bell and the NFL are also challenging the decision in court.

American Super Bowl ads have become an annual tradition for advertisers who try to outdo each other with increasingly elaborate commercials.

Image copyright Getty Images Image caption Super Bowl ads, like this one from 2003, have become an annual tradition for advertisers who try to outdo each other with increasingly elaborate commercials

Patricia Valladao, a CRTC spokeswoman, told the BBC the decision by the regulator to end simsub for the Super Bowl was made after months of broader consultations, and is a once-per-year exception to simsub.

Beyond the roughly 100 formal complaints received each year by the regulator, they also noticed "a lot of people going on Twitter ranting" about not being able to watch the American ads.

The Super Bowl is the most-viewed TV event in Canada and generates the highest advertising revenues of all of the live event programs that air on Bell Media stations.

In December, Bell and the NFL filed legal action with the Federal Court of Appeal arguing that the regulator has no jurisdiction to end simsub on a single program or to interfere with contracts already negotiated between the broadcaster and the league.

In an attempt to mitigate what the company is projecting as "significant" losses and tempt viewers into watching the game on their Canadian network, Bell Media is broadcasting the game on three of its channels, offering prizes - including a car - to viewers, and sending Canadian fans to a website where they can watch all the "best new" and "fan favourite" American ads.

And the NFL is publicly appealing to the federal government to overturn the decision before Sunday, warning the new policy threatens the relationship between the two countries.

Image copyright Getty Images Image caption The Atlanta Falcons will take on the New England Patriots in this year's Super Bowl.

"At a time when the future of the Canada-US relationship is in the headlines daily, we want the NFL-Canada relationship to continue to serve as a positive example - to government and to business - of what works," the league's executive vice-president, Mark Waller, said in a recent opinion piece.

With trade fears in the air and Mr Trump's ties to the NFL - he is friends with Patriots quarterback Tom Brady, and he recently appointed New York Jets owner Woody Johnson as UK ambassador - it is not an idle warning.

But so far Ottawa has said it respects the regulator's independence.

Meanwhile, time is ticking on the Hail Mary pass by Bell and the NFL.

Their court case will not be heard in time for Sunday's big game, but Bell Media is hopeful for a favourable ruling in time for the next NFL season.