Why were the war hawks eager to go to war with great britain in 1812?

Expansion--the War Hawks wanted to expand into Spanish Florida and the Northwest, held by Britain. 

The Napoleonic Wars were causing attacks on US ships and the British were sponsoring Indian raids on frontier lands. This angered Southern and Western politicians who saw this as an opportunity to expand US land holdings. Expanding US land holdings would increase resources and opportunities but also get European countries out of the Western Hemisphere.