Mother, Walsh Trott Chick Smith and Miles Calcraft Briginshaw Duffy will pitch against the Birmingham-based Palmer Hargreaves Wallis Tomlinson, the incumbent on the business for the past 14 years.
The review comes amid plans by the company to double its current UK ad budget to £6 million and to move the brand beyond its niche status.
Subaru currently has little significant advertising presence in the UK.
However, the arrival of the former BMW senior marketer Peter Kinnaird at the end of last year is expected to signal a more aggressive approach.
At present Subaru's share of the UK car market is modest. It sells around 10,000 cars a year in the UK and commands a loyal customer base. In the future, the company is looking to break into a broader market, selling more cars at lower margins.
In recent years, Subaru has exploited its successes in motorsport to boost UK sales. The manufacturer's high-performance Impreza model has scored a number of wins at the British rally championship.
Before the Impreza's arrival, Subaru concentrated its UK promotion on its Forester station wagon range, targeting upmarket rural drivers with high disposable incomes.
However, the Impreza has taken Subaru into new territory, putting the company into competition with the BMW 3 series as well as Audi, Honda and Mitsubishi.
"Subaru doesn't want to be seen as a niche brand, dri-ven only by farmers' wives and boy racers," an industry source said.