I only ask because I have a butt load available. Did a Google search and people said most 2x4 were fir?

I doubt it but they do make good kindling for fires.

Your basic 2x4 is SPF, meaning Spruce, Pine and  Fir. These are soft wood and would rot and soak in water no matter how much sealer you put on it. I would not use it to make lures.

Yeah you can use it to make lures with.  Is it ideal?  No, it will make things harder.  My dad made a couple with scrap 2X4's.  You can use just about any type of wood the biggest thing that will change is the tools you use.  For balsa sand paper will do a ton of the work for you.  With 2X4's you'll probably need some rasps.  I would suggest balsa, but if 2X4's is what you have go for it. 

As for sealing it once you have your blank with the weight in and wire or screw eyes in and ready for paint, put a coat of 30 min. 2 part epoxy on, paint, then seal that with a finish coat of epoxy.  The first coat seals the wood and gives a base for the paint, the second coat protects the paint.

Cool thanks guys its free wood if I get bored I might mess with it. If not fishable it can still decorate the Christmas tree lol

When you get down to it, it's worth the minor added expense to buy a specific kind of wood that has been kiln dried and has not been laying around on a job site absorbing moisture for who knows how long.  I use balsa, basswood, cedar, and paulownia to make baits, depending on the buoyancy I want in a specific design.  All of them are different as to how they cut, sand, and take finish.  Using odd scraps of pine or whatever is ok if you're just fooling around and want to try your hand at a crankbait.  When you get serious and want to advance your craft, you'll probably want to concentrate on one kind of wood and master how to make it into consistently good crankbaits.  The raw materials for a crankbait are neglidgeable compared to the value you add to them with your hand work, so it pays to use good stuff to begin with.

Basswood.......a fine grain in a strong, but quite light wood.  Excellent for shaping and carving.