The new partners have combined billings of £360m, taking EuroLab's total worldwide revenues to more than £1.4bn. The network operates not just in Europe, but also in Japan and North America.
The Spanish partner is Sapin's top independent media agency Cencomed. Launched in 1995, it has billings of more than £48m. Clients include UIP, Dreamworks and Spanish state lottery LAE.
In Russia, the new partner is Sovero Media, with billings of £17m with Pepsi Bottling Group, SAB Miller, Pernod Ricard and Electrolux as clients.
In Canada, Cossette Media, which bills £250m for clients including Coca Cola, Nike Canada and Saturn SAAB, has also joined, as has Creative Media Services with billings of £13m and a client list that includes Adidas, Hyundai and L'Oreal.
Nick Lockett, chairman of EuroLab, said: "International advertisers are increasingly frustrated by the lack of choice offered in the international media arena.
"We have put together some of the best independent media companies to provide a compelling alternative to the multinational media groups."