OK, just for clarification, the "intake" is the part that is bolted into the hull and the "suction housing" is the part that is removeable and contains the shaft, impeller, etc.
Best suggestion would be to get some spray carb or brake cleaner and soak the gasket. Use a razor knife, utility blade or gasket scraper to carefully slice between gasket and housing. Once you have a section started, you might be able to use a stiff putty knife to continue separating the gasket.
Avoid the temptation to use power tools! You need to keep a nice flat surface to insure proper gasket sealing.