Hawaiian volcanoes are not located at plate margins while Cascade volcanoes are a result of activity at a subduction zone. The Hawaiian volcanoes are located above a fixed hot spot or hole in the middle of the Pacific plate. Think of the the hot spot as melting a hole in the plate and sending up magma through it. Also Hawaiian volcanoes are also shield volcanoes with quiet eruptions while the Cascades are composite volcanoes which are explosive (think Mt St Helens)